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DBD::SQLite(3) User Contributed Perl Documentation DBD::SQLite(3)
NAME
DBD::SQLite - Self-contained RDBMS in a DBI Driver
SYNOPSIS
use DBI;
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");
DESCRIPTION
SQLite is a public domain file-based relational database engine that you can find at
<http://www.sqlite.org/>.
DBD::SQLite is a Perl DBI driver for SQLite, that includes the entire thing in the
distribution. So in order to get a fast transaction capable RDBMS working for your perl
project you simply have to install this module, and nothing else.
SQLite supports the following features:
Implements a large subset of SQL92
See <http://www.sqlite.org/lang.html> for details.
A complete DB in a single disk file
Everything for your database is stored in a single disk file, making it easier to move
things around than with DBD::CSV.
Atomic commit and rollback
Yes, DBD::SQLite is small and light, but it supports full transactions!
Extensible
User-defined aggregate or regular functions can be registered with the SQL parser.
There's lots more to it, so please refer to the docs on the SQLite web page, listed above,
for SQL details. Also refer to DBI for details on how to use DBI itself. The API works
like every DBI module does. However, currently many statement attributes are not
implemented or are limited by the typeless nature of the SQLite database.
NOTABLE DIFFERENCES FROM OTHER DRIVERS
Database Name Is A File Name
SQLite creates a file per a database. You should pass the "path" of the database file
(with or without a parent directory) in the DBI connection string (as a database "name"):
my $dbh = DBI->connect("dbi:SQLite:dbname=$dbfile","","");
The file is opened in read/write mode, and will be created if it does not exist yet.
Although the database is stored in a single file, the directory containing the database
file must be writable by SQLite because the library will create several temporary files
there.
If the filename $dbfile is ":memory:", then a private, temporary in-memory database is
created for the connection. This in-memory database will vanish when the database
connection is closed. It is handy for your library tests.
Note that future versions of SQLite might make use of additional special filenames that
begin with the ":" character. It is recommended that when a database filename actually
does begin with a ":" character you should prefix the filename with a pathname such as
"./" to avoid ambiguity.
If the filename $dbfile is an empty string, then a private, temporary on-disk database
will be created. This private database will be automatically deleted as soon as the
database connection is closed.
DBD::SQLite And File::Temp
When you use File::Temp to create a temporary file/directory for SQLite databases, you
need to remember:
tempfile may be locked exclusively
You may want to use "tempfile()" to create a temporary database filename for
DBD::SQLite, but as noted in File::Temp's POD, this file may have an exclusive lock
under some operating systems (notably Mac OSX), and result in a "database is locked"
error. To avoid this, set EXLOCK option to false when you call tempfile().
($fh, $filename) = tempfile($template, EXLOCK => 0);
CLEANUP may not work unless a database is disconnected
When you set CLEANUP option to true when you create a temporary directory with
"tempdir()" or "newdir()", you may have to disconnect databases explicitly before the
temporary directory is gone (notably under MS Windows).
(The above is quoted from the pod of File::Temp.)
If you don't need to keep or share a temporary database, use ":memory:" database instead.
It's much handier and cleaner for ordinary testing.
Accessing A Database With Other Tools
To access the database from the command line, try using "dbish" which comes with the
DBI::Shell module. Just type:
dbish dbi:SQLite:foo.db
On the command line to access the file foo.db.
Alternatively you can install SQLite from the link above without conflicting with
DBD::SQLite and use the supplied "sqlite3" command line tool.
Blobs
As of version 1.11, blobs should "just work" in SQLite as text columns. However this will
cause the data to be treated as a string, so SQL statements such as length(x) will return
the length of the column as a NUL terminated string, rather than the size of the blob in
bytes. In order to store natively as a BLOB use the following code:
use DBI qw(:sql_types);
my $dbh = DBI->connect("dbi:SQLite:dbfile","","");
my $blob = `cat foo.jpg`;
my $sth = $dbh->prepare("INSERT INTO mytable VALUES (1, ?)");
$sth->bind_param(1, $blob, SQL_BLOB);
$sth->execute();
And then retrieval just works:
$sth = $dbh->prepare("SELECT * FROM mytable WHERE id = 1");
$sth->execute();
my $row = $sth->fetch;
my $blobo = $row->[1];
# now $blobo == $blob
Functions And Bind Parameters
As of this writing, a SQL that compares a return value of a function with a numeric bind
value like this doesn't work as you might expect.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);
This is because DBD::SQLite assumes that all the bind values are text (and should be
quoted) by default. Thus the above statement becomes like this while executing:
SELECT bar FROM foo GROUP BY bar HAVING count(*) > "5";
There are three workarounds for this.
Use bind_param() explicitly
As shown above in the "BLOB" section, you can always use "bind_param()" to tell the
type of a bind value.
use DBI qw(:sql_types); # Don't forget this
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->bind_param(1, 5, SQL_INTEGER);
$sth->execute();
Add zero to make it a number
This is somewhat weird, but works anyway.
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > (? + 0);
});
$sth->execute(5);
Set "sqlite_see_if_its_a_number" database handle attribute
As of version 1.32_02, you can use "sqlite_see_if_its_a_number" to let DBD::SQLite to
see if the bind values are numbers or not.
$dbh->{sqlite_see_if_its_a_number} = 1;
my $sth = $dbh->prepare(q{
SELECT bar FROM foo GROUP BY bar HAVING count(*) > ?;
});
$sth->execute(5);
You can set it to true when you connect to a database.
my $dbh = DBI->connect('dbi:SQLite:foo', undef, undef, {
AutoCommit => 1,
RaiseError => 1,
sqlite_see_if_its_a_number => 1,
});
This is the most straightforward solution, but as noted above, existing data in your
databases created by DBD::SQLite have not always been stored as numbers, so this
*might* cause other obscure problems. Use this sparingly when you handle existing
databases. If you handle databases created by other tools like native "sqlite3"
command line tool, this attribute would help you.
Placeholders
SQLite supports several placeholder expressions, including "?" and ":AAAA". Consult the
DBI and sqlite documentation for details.
<http://www.sqlite.org/lang_expr.html#varparam>
Note that a question mark actually means a next unused (numbered) placeholder. You're
advised not to use it with other (numbered or named) placeholders to avoid confusion.
my $sth = $dbh->prepare(
'update TABLE set a=?1 where b=?2 and a IS NOT ?1'
);
$sth->execute(1, 2);
Foreign Keys
BE PREPARED! WOLVES APPROACH!!
SQLite has started supporting foreign key constraints since 3.6.19 (released on Oct 14,
2009; bundled in DBD::SQLite 1.26_05). To be exact, SQLite has long been able to parse a
schema with foreign keys, but the constraints has not been enforced. Now you can issue a
pragma actually to enable this feature and enforce the constraints.
To do this, issue the following pragma (see below), preferably as soon as you connect to a
database and you're not in a transaction:
$dbh->do("PRAGMA foreign_keys = ON");
And you can explicitly disable the feature whenever you like by turning the pragma off:
$dbh->do("PRAGMA foreign_keys = OFF");
As of this writing, this feature is disabled by default by the sqlite team, and by us, to
secure backward compatibility, as this feature may break your applications, and actually
broke some for us. If you have used a schema with foreign key constraints but haven't
cared them much and supposed they're always ignored for SQLite, be prepared, and please do
extensive testing to ensure that your applications will continue to work when the foreign
keys support is enabled by default. It is very likely that the sqlite team will turn it
default-on in the future, and we plan to do it NO LATER THAN they do so.
See <http://www.sqlite.org/foreignkeys.html> for details.
Pragma
SQLite has a set of "Pragma"s to modify its operation or to query for its internal data.
These are specific to SQLite and are not likely to work with other DBD libraries, but you
may find some of these are quite useful, including:
journal_mode
You can use this pragma to change the journal mode for SQLite databases, maybe for
better performance, or for compatibility.
Its default mode is "DELETE", which means SQLite uses a rollback journal to implement
transactions, and the journal is deleted at the conclusion of each transaction. If you
use "TRUNCATE" instead of "DELETE", the journal will be truncated, which is usually
much faster.
A "WAL" (write-ahead log) mode is introduced as of SQLite 3.7.0. This mode is
persistent, and it stays in effect even after closing and reopening the database. In
other words, once the "WAL" mode is set in an application or in a test script, the
database becomes inaccessible by older clients. This tends to be an issue when you use
a system "sqlite3" executable under a conservative operating system.
To fix this, You need to issue "PRAGMA journal_mode = DELETE" (or "TRUNCATE")
beforehand, or install a newer version of "sqlite3".
legacy_file_format
If you happen to need to create a SQLite database that will also be accessed by a very
old SQLite client (prior to 3.3.0 released in Jan. 2006), you need to set this pragma
to ON before you create a database.
reverse_unordered_selects
You can set this pragma to ON to reverse the order of results of SELECT statements
without an ORDER BY clause so that you can see if applications are making invalid
assumptions about the result order.
Note that SQLite 3.7.15 (bundled with DBD::SQLite 1.38_02) enhanced its query
optimizer and the order of results of a SELECT statement without an ORDER BY clause
may be different from the one of the previous versions.
synchronous
You can set set this pragma to OFF to make some of the operations in SQLite faster
with a possible risk of database corruption in the worst case. See also "Performance"
section below.
See <http://www.sqlite.org/pragma.html> for more details.
Transactions
DBI/DBD::SQLite's transactions may be a bit confusing. They behave differently according
to the status of the "AutoCommit" flag:
When the AutoCommit flag is on
You're supposed to always use the auto-commit mode, except you explicitly begin a
transaction, and when the transaction ended, you're supposed to go back to the auto-
commit mode. To begin a transaction, call "begin_work" method, or issue a "BEGIN"
statement. To end it, call "commit/rollback" methods, or issue the corresponding
statements.
$dbh->{AutoCommit} = 1;
$dbh->begin_work; # or $dbh->do('BEGIN TRANSACTION');
# $dbh->{AutoCommit} is turned off temporarily during a transaction;
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} is turned on again;
When the AutoCommit flag is off
You're supposed to always use the transactional mode, until you explicitly turn on the
AutoCommit flag. You can explicitly issue a "BEGIN" statement (only when an actual
transaction has not begun yet) but you're not allowed to call "begin_work" method (if
you don't issue a "BEGIN", it will be issued internally). You can commit or roll it
back freely. Another transaction will automatically begins if you execute another
statement.
$dbh->{AutoCommit} = 0;
# $dbh->do('BEGIN TRANSACTION') is not necessary, but possible
...
$dbh->commit; # or $dbh->do('COMMIT');
# $dbh->{AutoCommit} stays intact;
$dbh->{AutoCommit} = 1; # ends the transactional mode
This "AutoCommit" mode is independent from the autocommit mode of the internal SQLite
library, which always begins by a "BEGIN" statement, and ends by a "COMMIT" or a
<ROLLBACK>.
Transaction and Database Locking
The default transaction behavior of SQLite is "deferred", that means, locks are not
acquired until the first read or write operation, and thus it is possible that another
thread or process could create a separate transaction and write to the database after the
"BEGIN" on the current thread has executed, and eventually cause a "deadlock". To avoid
this, DBD::SQLite internally issues a "BEGIN IMMEDIATE" when you begin a transaction by
"begin_work" or under the "AutoCommit" mode (since 1.38_01).
If you really need to turn off this feature for some reasons, set
"sqlite_use_immediate_transaction" database handle attribute to false, and the default
"deferred" transaction will be used.
my $dbh = DBI->connect("dbi:SQLite::memory:", "", "", {
sqlite_use_immediate_transaction => 0,
});
See <http://sqlite.org/lockingv3.html> for locking details.
"$sth->finish" and Transaction Rollback
As the DBI doc says, you almost certainly do not need to call "finish" in DBI method if
you fetch all rows (probably in a loop). However, there are several exceptions to this
rule, and rolling-back of an unfinished "SELECT" statement is one of such exceptional
cases.
SQLite prohibits "ROLLBACK" of unfinished "SELECT" statements in a transaction (See
<http://sqlite.org/lang_transaction.html> for details). So you need to call "finish"
before you issue a rollback.
$sth = $dbh->prepare("SELECT * FROM t");
$dbh->begin_work;
eval {
$sth->execute;
$row = $sth->fetch;
...
die "For some reason";
...
};
if($@) {
$sth->finish; # You need this for SQLite
$dbh->rollback;
} else {
$dbh->commit;
}
Processing Multiple Statements At A Time
DBI's statement handle is not supposed to process multiple statements at a time. So if you
pass a string that contains multiple statements (a "dump") to a statement handle (via
"prepare" or "do"), DBD::SQLite only processes the first statement, and discards the rest.
Since 1.30_01, you can retrieve those ignored (unprepared) statements via
"$sth->{sqlite_unprepared_statements}". It usually contains nothing but white spaces, but
if you really care, you can check this attribute to see if there's anything left undone.
Also, if you set a "sqlite_allow_multiple_statements" attribute of a database handle to
true when you connect to a database, "do" method automatically checks the
"sqlite_unprepared_statements" attribute, and if it finds anything undone (even if what's
left is just a single white space), it repeats the process again, to the end.
Performance
SQLite is fast, very fast. Matt processed his 72MB log file with it, inserting the data
(400,000+ rows) by using transactions and only committing every 1000 rows (otherwise the
insertion is quite slow), and then performing queries on the data.
Queries like count(*) and avg(bytes) took fractions of a second to return, but what
surprised him most of all was:
SELECT url, count(*) as count
FROM access_log
GROUP BY url
ORDER BY count desc
LIMIT 20
To discover the top 20 hit URLs on the site (<http://axkit.org>), and it returned within 2
seconds. He was seriously considering switching his log analysis code to use this little
speed demon!
Oh yeah, and that was with no indexes on the table, on a 400MHz PIII.
For best performance be sure to tune your hdparm settings if you are using linux. Also you
might want to set:
PRAGMA synchronous = OFF
Which will prevent sqlite from doing fsync's when writing (which slows down non-
transactional writes significantly) at the expense of some peace of mind. Also try playing
with the cache_size pragma.
The memory usage of SQLite can also be tuned using the cache_size pragma.
$dbh->do("PRAGMA cache_size = 800000");
The above will allocate 800M for DB cache; the default is 2M. Your sweet spot probably
lies somewhere in between.
DRIVER PRIVATE ATTRIBUTES
Database Handle Attributes
sqlite_version
Returns the version of the SQLite library which DBD::SQLite is using, e.g., "2.8.0".
Can only be read.
sqlite_unicode
If set to a true value, DBD::SQLite will turn the UTF-8 flag on for all text strings
coming out of the database (this feature is currently disabled for perl < 5.8.5). For
more details on the UTF-8 flag see perlunicode. The default is for the UTF-8 flag to
be turned off.
Also note that due to some bizarreness in SQLite's type system (see
<http://www.sqlite.org/datatype3.html>), if you want to retain blob-style behavior for
some columns under "$dbh->{sqlite_unicode} = 1" (say, to store images in the
database), you have to state so explicitly using the 3-argument form of "bind_param"
in DBI when doing updates:
use DBI qw(:sql_types);
$dbh->{sqlite_unicode} = 1;
my $sth = $dbh->prepare("INSERT INTO mytable (blobcolumn) VALUES (?)");
# Binary_data will be stored as is.
$sth->bind_param(1, $binary_data, SQL_BLOB);
Defining the column type as "BLOB" in the DDL is not sufficient.
This attribute was originally named as "unicode", and renamed to "sqlite_unicode" for
integrity since version 1.26_06. Old "unicode" attribute is still accessible but will
be deprecated in the near future.
sqlite_allow_multiple_statements
If you set this to true, "do" method will process multiple statements at one go. This
may be handy, but with performance penalty. See above for details.
sqlite_use_immediate_transaction
If you set this to true, DBD::SQLite tries to issue a "begin immediate transaction"
(instead of "begin transaction") when necessary. See above for details.
As of version 1.38_01, this attribute is set to true by default. If you really need
to use "deferred" transactions for some reasons, set this to false explicitly.
sqlite_see_if_its_a_number
If you set this to true, DBD::SQLite tries to see if the bind values are number or
not, and does not quote if they are numbers. See above for details.
Statement Handle Attributes
sqlite_unprepared_statements
Returns an unprepared part of the statement you pass to "prepare". Typically this
contains nothing but white spaces after a semicolon. See above for details.
METHODS
See also to the DBI documentation for the details of other common methods.
table_info
$sth = $dbh->table_info(undef, $schema, $table, $type, \%attr);
Returns all tables and schemas (databases) as specified in "table_info" in DBI. The
schema and table arguments will do a "LIKE" search. You can specify an ESCAPE character by
including an 'Escape' attribute in \%attr. The $type argument accepts a comma separated
list of the following types 'TABLE', 'VIEW', 'LOCAL TEMPORARY' and 'SYSTEM TABLE' (by
default all are returned). Note that a statement handle is returned, and not a direct
list of tables.
The following fields are returned:
TABLE_CAT: Always NULL, as SQLite does not have the concept of catalogs.
TABLE_SCHEM: The name of the schema (database) that the table or view is in. The default
schema is 'main', temporary tables are in 'temp' and other databases will be in the name
given when the database was attached.
TABLE_NAME: The name of the table or view.
TABLE_TYPE: The type of object returned. Will be one of 'TABLE', 'VIEW', 'LOCAL TEMPORARY'
or 'SYSTEM TABLE'.
primary_key, primary_key_info
@names = $dbh->primary_key(undef, $schema, $table);
$sth = $dbh->primary_key_info(undef, $schema, $table, \%attr);
You can retrieve primary key names or more detailed information. As noted above, SQLite
does not have the concept of catalogs, so the first argument of the methods is usually
"undef", and you'll usually set "undef" for the second one (unless you want to know the
primary keys of temporary tables).
foreign_key_info
$sth = $dbh->foreign_key_info(undef, $pk_schema, $pk_table,
undef, $fk_schema, $fk_table);
Returns information about foreign key constraints, as specified in "foreign_key_info" in
DBI, but with some limitations :
o information in rows returned by the $sth is incomplete with respect to the
"foreign_key_info" in DBI specification. All requested fields are present, but the
content is "undef" for some of them.
The following nonempty fields are returned :
PKTABLE_NAME: The primary (unique) key table identifier.
PKCOLUMN_NAME: The primary (unique) key column identifier.
FKTABLE_NAME: The foreign key table identifier.
FKCOLUMN_NAME: The foreign key column identifier.
KEY_SEQ: The column sequence number (starting with 1), when several columns belong to a
same constraint.
UPDATE_RULE: The referential action for the UPDATE rule. The following codes are defined:
CASCADE 0
RESTRICT 1
SET NULL 2
NO ACTION 3
SET DEFAULT 4
Default is 3 ('NO ACTION').
DELETE_RULE: The referential action for the DELETE rule. The codes are the same as for
UPDATE_RULE.
Unfortunately, the DEFERRABILITY field is always "undef"; as a matter of fact,
deferrability clauses are supported by SQLite, but they can't be reported because the
"PRAGMA foreign_key_list" tells nothing about them.
UNIQUE_OR_PRIMARY: Whether the column is primary or unique.
Note: foreign key support in SQLite must be explicitly turned on through a "PRAGMA"
command; see "Foreign keys" earlier in this manual.
ping
my $bool = $dbh->ping;
returns true if the database file exists (or the database is in-memory), and the database
connection is active.
DRIVER PRIVATE METHODS
The following methods can be called via the func() method with a little tweak, but the use
of func() method is now discouraged by the DBI author for various reasons (see DBI's
document
<http://search.cpan.org/dist/DBI/lib/DBI/DBD.pm#Using_install_method()_to_expose_driver-private_methods>
for details). So, if you're using DBI >= 1.608, use these "sqlite_" methods. If you need
to use an older DBI, you can call these like this:
$dbh->func( ..., "(method name without sqlite_ prefix)" );
Exception: "sqlite_trace" should always be called as is, even with "func()" method (to
avoid conflict with DBI's trace() method).
$dbh->func( ..., "sqlite_trace");
$dbh->sqlite_last_insert_rowid()
This method returns the last inserted rowid. If you specify an INTEGER PRIMARY KEY as the
first column in your table, that is the column that is returned. Otherwise, it is the
hidden ROWID column. See the sqlite docs for details.
Generally you should not be using this method. Use the DBI last_insert_id method instead.
The usage of this is:
$h->last_insert_id($catalog, $schema, $table_name, $field_name [, \%attr ])
Running "$h->last_insert_id("","","","")" is the equivalent of running
"$dbh->sqlite_last_insert_rowid()" directly.
$dbh->sqlite_db_filename()
Retrieve the current (main) database filename. If the database is in-memory or temporary,
this returns "undef".
$dbh->sqlite_busy_timeout()
Retrieve the current busy timeout.
$dbh->sqlite_busy_timeout( $ms )
Set the current busy timeout. The timeout is in milliseconds.
$dbh->sqlite_create_function( $name, $argc, $code_ref )
This method will register a new function which will be usable in an SQL query. The
method's parameters are:
$name
The name of the function. This is the name of the function as it will be used from
SQL.
$argc
The number of arguments taken by the function. If this number is -1, the function can
take any number of arguments.
$code_ref
This should be a reference to the function's implementation.
For example, here is how to define a now() function which returns the current number of
seconds since the epoch:
$dbh->sqlite_create_function( 'now', 0, sub { return time } );
After this, it could be use from SQL as:
INSERT INTO mytable ( now() );
REGEXP function
SQLite includes syntactic support for an infix operator 'REGEXP', but without any
implementation. The "DBD::SQLite" driver automatically registers an implementation that
performs standard perl regular expression matching, using current locale. So for example
you can search for words starting with an 'A' with a query like
SELECT * from table WHERE column REGEXP '\bA\w+'
If you want case-insensitive searching, use perl regex flags, like this :
SELECT * from table WHERE column REGEXP '(?i:\bA\w+)'
The default REGEXP implementation can be overridden through the "create_function" API
described above.
Note that regexp matching will not use SQLite indices, but will iterate over all rows, so
it could be quite costly in terms of performance.
$dbh->sqlite_create_collation( $name, $code_ref )
This method manually registers a new function which will be usable in an SQL query as a
COLLATE option for sorting. Such functions can also be registered automatically on demand:
see section "COLLATION FUNCTIONS" below.
The method's parameters are:
$name
The name of the function exposed to SQL.
$code_ref
Reference to the function's implementation. The driver will check that this is a
proper sorting function.
$dbh->sqlite_collation_needed( $code_ref )
This method manually registers a callback function that will be invoked whenever an
undefined collation sequence is required from an SQL statement. The callback is invoked as
$code_ref->($dbh, $collation_name)
and should register the desired collation using "sqlite_create_collation".
An initial callback is already registered by "DBD::SQLite", so for most common cases it
will be simpler to just add your collation sequences in the %DBD::SQLite::COLLATION hash
(see section "COLLATION FUNCTIONS" below).
$dbh->sqlite_create_aggregate( $name, $argc, $pkg )
This method will register a new aggregate function which can then be used from SQL. The
method's parameters are:
$name
The name of the aggregate function, this is the name under which the function will be
available from SQL.
$argc
This is an integer which tells the SQL parser how many arguments the function takes.
If that number is -1, the function can take any number of arguments.
$pkg
This is the package which implements the aggregator interface.
The aggregator interface consists of defining three methods:
new()
This method will be called once to create an object which should be used to aggregate
the rows in a particular group. The step() and finalize() methods will be called upon
the reference return by the method.
step(@_)
This method will be called once for each row in the aggregate.
finalize()
This method will be called once all rows in the aggregate were processed and it should
return the aggregate function's result. When there is no rows in the aggregate,
finalize() will be called right after new().
Here is a simple aggregate function which returns the variance (example adapted from
pysqlite):
package variance;
sub new { bless [], shift; }
sub step {
my ( $self, $value ) = @_;
push @$self, $value;
}
sub finalize {
my $self = $_[0];
my $n = @$self;
# Variance is NULL unless there is more than one row
return undef unless $n || $n == 1;
my $mu = 0;
foreach my $v ( @$self ) {
$mu += $v;
}
$mu /= $n;
my $sigma = 0;
foreach my $v ( @$self ) {
$sigma += ($v - $mu)**2;
}
$sigma = $sigma / ($n - 1);
return $sigma;
}
$dbh->sqlite_create_aggregate( "variance", 1, 'variance' );
The aggregate function can then be used as:
SELECT group_name, variance(score)
FROM results
GROUP BY group_name;
For more examples, see the DBD::SQLite::Cookbook.
$dbh->sqlite_progress_handler( $n_opcodes, $code_ref )
This method registers a handler to be invoked periodically during long running calls to
SQLite.
An example use for this interface is to keep a GUI updated during a large query. The
parameters are:
$n_opcodes
The progress handler is invoked once for every $n_opcodes virtual machine opcodes in
SQLite.
$code_ref
Reference to the handler subroutine. If the progress handler returns non-zero, the
SQLite operation is interrupted. This feature can be used to implement a "Cancel"
button on a GUI dialog box.
Set this argument to "undef" if you want to unregister a previous progress handler.
$dbh->sqlite_commit_hook( $code_ref )
This method registers a callback function to be invoked whenever a transaction is
committed. Any callback set by a previous call to "sqlite_commit_hook" is overridden. A
reference to the previous callback (if any) is returned. Registering an "undef" disables
the callback.
When the commit hook callback returns zero, the commit operation is allowed to continue
normally. If the callback returns non-zero, then the commit is converted into a rollback
(in that case, any attempt to explicitly call "$dbh->rollback()" afterwards would yield an
error).
$dbh->sqlite_rollback_hook( $code_ref )
This method registers a callback function to be invoked whenever a transaction is rolled
back. Any callback set by a previous call to "sqlite_rollback_hook" is overridden. A
reference to the previous callback (if any) is returned. Registering an "undef" disables
the callback.
$dbh->sqlite_update_hook( $code_ref )
This method registers a callback function to be invoked whenever a row is updated,
inserted or deleted. Any callback set by a previous call to "sqlite_update_hook" is
overridden. A reference to the previous callback (if any) is returned. Registering an
"undef" disables the callback.
The callback will be called as
$code_ref->($action_code, $database, $table, $rowid)
where
$action_code
is an integer equal to either "DBD::SQLite::INSERT", "DBD::SQLite::DELETE" or
"DBD::SQLite::UPDATE" (see "Action Codes");
$database
is the name of the database containing the affected row;
$table
is the name of the table containing the affected row;
$rowid
is the unique 64-bit signed integer key of the affected row within that table.
$dbh->sqlite_set_authorizer( $code_ref )
This method registers an authorizer callback to be invoked whenever SQL statements are
being compiled by the "prepare" in DBI method. The authorizer callback should return
"DBD::SQLite::OK" to allow the action, "DBD::SQLite::IGNORE" to disallow the specific
action but allow the SQL statement to continue to be compiled, or "DBD::SQLite::DENY" to
cause the entire SQL statement to be rejected with an error. If the authorizer callback
returns any other value, then "prepare" call that triggered the authorizer will fail with
an error message.
An authorizer is used when preparing SQL statements from an untrusted source, to ensure
that the SQL statements do not try to access data they are not allowed to see, or that
they do not try to execute malicious statements that damage the database. For example, an
application may allow a user to enter arbitrary SQL queries for evaluation by a database.
But the application does not want the user to be able to make arbitrary changes to the
database. An authorizer could then be put in place while the user-entered SQL is being
prepared that disallows everything except SELECT statements.
The callback will be called as
$code_ref->($action_code, $string1, $string2, $database, $trigger_or_view)
where
$action_code
is an integer that specifies what action is being authorized (see "Action Codes").
$string1, $string2
are strings that depend on the action code (see "Action Codes").
$database
is the name of the database ("main", "temp", etc.) if applicable.
$trigger_or_view
is the name of the inner-most trigger or view that is responsible for the access
attempt, or "undef" if this access attempt is directly from top-level SQL code.
$dbh->sqlite_backup_from_file( $filename )
This method accesses the SQLite Online Backup API, and will take a backup of the named
database file, copying it to, and overwriting, your current database connection. This can
be particularly handy if your current connection is to the special :memory: database, and
you wish to populate it from an existing DB.
$dbh->sqlite_backup_to_file( $filename )
This method accesses the SQLite Online Backup API, and will take a backup of the currently
connected database, and write it out to the named file.
$dbh->sqlite_enable_load_extension( $bool )
Calling this method with a true value enables loading (external) sqlite3 extensions. After
the call, you can load extensions like this:
$dbh->sqlite_enable_load_extension(1);
$sth = $dbh->prepare("select load_extension('libsqlitefunctions.so')")
or die "Cannot prepare: " . $dbh->errstr();
$dbh->sqlite_load_extension( $file, $proc )
Loading an extension by a select statement (with the "load_extension" sqlite3 function
like above) has some limitations. If you need to, say, create other functions from an
extension, use this method. $file (a path to the extension) is mandatory, and $proc (an
entry point name) is optional. You need to call "sqlite_enable_load_extension" before
calling "sqlite_load_extension".
$dbh->sqlite_trace( $code_ref )
This method registers a trace callback to be invoked whenever SQL statements are being
run.
The callback will be called as
$code_ref->($statement)
where
$statement
is a UTF-8 rendering of the SQL statement text as the statement first begins
executing.
Additional callbacks might occur as each triggered subprogram is entered. The callbacks
for triggers contain a UTF-8 SQL comment that identifies the trigger.
See also "TRACING" in DBI for better tracing options.
$dbh->sqlite_profile( $code_ref )
This method registers a profile callback to be invoked whenever a SQL statement finishes.
The callback will be called as
$code_ref->($statement, $elapsed_time)
where
$statement
is the original statement text (without bind parameters).
$elapsed_time
is an estimate of wall-clock time of how long that statement took to run (in
milliseconds).
This method is considered experimental and is subject to change in future versions of
SQLite.
See also DBI::Profile for better profiling options.
$dbh->sqlite_table_column_metadata( $dbname, $tablename, $columnname )
is for internal use only.
DBD::SQLite::compile_options()
Returns an array of compile options (available since sqlite 3.6.23, bundled in DBD::SQLite
1.30_01), or an empty array if the bundled library is old or compiled with
SQLITE_OMIT_COMPILEOPTION_DIAGS.
DBD::SQLite::sqlite_status()
Returns a hash reference that holds a set of status information of SQLite runtime such as
memory usage or page cache usage (see
<http://www.sqlite.org/c3ref/c_status_malloc_count.html> for details). Each of the entry
contains the current value and the highwater value.
my $status = DBD::SQLite::sqlite_status();
my $cur = $status->{memory_used}{current};
my $high = $status->{memory_used}{highwater};
You may also pass 0 as an argument to reset the status.
$dbh->sqlite_db_status()
Returns a hash reference that holds a set of status information of database connection
such as cache usage. See <http://www.sqlite.org/c3ref/c_dbstatus_options.html> for
details. You may also pass 0 as an argument to reset the status.
$sth->sqlite_st_status()
Returns a hash reference that holds a set of status information of SQLite statement handle
such as full table scan count. See <http://www.sqlite.org/c3ref/c_stmtstatus_counter.html>
for details. Statement status only holds the current value.
my $status = $sth->sqlite_st_status();
my $cur = $status->{fullscan_step};
You may also pass 0 as an argument to reset the status.
DRIVER CONSTANTS
A subset of SQLite C constants are made available to Perl, because they may be needed when
writing hooks or authorizer callbacks. For accessing such constants, the "DBD::SQLite"
module must be explicitly "use"d at compile time. For example, an authorizer that forbids
any DELETE operation would be written as follows :
use DBD::SQLite;
$dbh->sqlite_set_authorizer(sub {
my $action_code = shift;
return $action_code == DBD::SQLite::DELETE ? DBD::SQLite::DENY
: DBD::SQLite::OK;
});
The list of constants implemented in "DBD::SQLite" is given below; more information can be
found ad at <http://www.sqlite.org/c3ref/constlist.html>.
Authorizer Return Codes
OK
DENY
IGNORE
Action Codes
The "set_authorizer" method registers a callback function that is invoked to authorize
certain SQL statement actions. The first parameter to the callback is an integer code that
specifies what action is being authorized. The second and third parameters to the callback
are strings, the meaning of which varies according to the action code. Below is the list
of action codes, together with their associated strings.
# constant string1 string2
# ======== ======= =======
CREATE_INDEX Index Name Table Name
CREATE_TABLE Table Name undef
CREATE_TEMP_INDEX Index Name Table Name
CREATE_TEMP_TABLE Table Name undef
CREATE_TEMP_TRIGGER Trigger Name Table Name
CREATE_TEMP_VIEW View Name undef
CREATE_TRIGGER Trigger Name Table Name
CREATE_VIEW View Name undef
DELETE Table Name undef
DROP_INDEX Index Name Table Name
DROP_TABLE Table Name undef
DROP_TEMP_INDEX Index Name Table Name
DROP_TEMP_TABLE Table Name undef
DROP_TEMP_TRIGGER Trigger Name Table Name
DROP_TEMP_VIEW View Name undef
DROP_TRIGGER Trigger Name Table Name
DROP_VIEW View Name undef
INSERT Table Name undef
PRAGMA Pragma Name 1st arg or undef
READ Table Name Column Name
SELECT undef undef
TRANSACTION Operation undef
UPDATE Table Name Column Name
ATTACH Filename undef
DETACH Database Name undef
ALTER_TABLE Database Name Table Name
REINDEX Index Name undef
ANALYZE Table Name undef
CREATE_VTABLE Table Name Module Name
DROP_VTABLE Table Name Module Name
FUNCTION undef Function Name
SAVEPOINT Operation Savepoint Name
COLLATION FUNCTIONS
Definition
SQLite v3 provides the ability for users to supply arbitrary comparison functions, known
as user-defined "collation sequences" or "collating functions", to be used for comparing
two text values. <http://www.sqlite.org/datatype3.html#collation> explains how collations
are used in various SQL expressions.
Builtin collation sequences
The following collation sequences are builtin within SQLite :
BINARY
Compares string data using memcmp(), regardless of text encoding.
NOCASE
The same as binary, except the 26 upper case characters of ASCII are folded to their
lower case equivalents before the comparison is performed. Note that only ASCII
characters are case folded. SQLite does not attempt to do full UTF case folding due to
the size of the tables required.
RTRIM
The same as binary, except that trailing space characters are ignored.
In addition, "DBD::SQLite" automatically installs the following collation sequences :
perl
corresponds to the Perl "cmp" operator
perllocale
Perl "cmp" operator, in a context where "use locale" is activated.
Usage
You can write for example
CREATE TABLE foo(
txt1 COLLATE perl,
txt2 COLLATE perllocale,
txt3 COLLATE nocase
)
or
SELECT * FROM foo ORDER BY name COLLATE perllocale
Unicode handling
If the attribute "$dbh->{sqlite_unicode}" is set, strings coming from the database and
passed to the collation function will be properly tagged with the utf8 flag; but this only
works if the "sqlite_unicode" attribute is set before the first call to a perl collation
sequence . The recommended way to activate unicode is to set the parameter at connection
time :
my $dbh = DBI->connect(
"dbi:SQLite:dbname=foo", "", "",
{
RaiseError => 1,
sqlite_unicode => 1,
}
);
Adding user-defined collations
The native SQLite API for adding user-defined collations is exposed through methods
"sqlite_create_collation" and "sqlite_collation_needed".
To avoid calling these functions every time a $dbh handle is created, "DBD::SQLite" offers
a simpler interface through the %DBD::SQLite::COLLATION hash : just insert your own
collation functions in that hash, and whenever an unknown collation name is encountered in
SQL, the appropriate collation function will be loaded on demand from the hash. For
example, here is a way to sort text values regardless of their accented characters :
use DBD::SQLite;
$DBD::SQLite::COLLATION{no_accents} = sub {
my ( $a, $b ) = map lc, @_;
tr[XXXXXXXXXXXXXXXXXXXXXXXXXXXX]
[aaaaaacdeeeeiiiinoooooouuuuy] for $a, $b;
$a cmp $b;
};
my $dbh = DBI->connect("dbi:SQLite:dbname=dbfile");
my $sql = "SELECT ... FROM ... ORDER BY ... COLLATE no_accents");
my $rows = $dbh->selectall_arrayref($sql);
The builtin "perl" or "perllocale" collations are predefined in that same hash.
The COLLATION hash is a global registry within the current process; hence there is a risk
of undesired side-effects. Therefore, to prevent action at distance, the hash is
implemented as a "write-only" hash, that will happily accept new entries, but will raise
an exception if any attempt is made to override or delete a existing entry (including the
builtin "perl" and "perllocale").
If you really, really need to change or delete an entry, you can always grab the tied
object underneath %DBD::SQLite::COLLATION --- but don't do that unless you really know
what you are doing. Also observe that changes in the global hash will not modify existing
collations in existing database handles: it will only affect new requests for collations.
In other words, if you want to change the behaviour of a collation within an existing
$dbh, you need to call the "create_collation" method directly.
FULLTEXT SEARCH
The FTS extension module within SQLite allows users to create special tables with a built-
in full-text index (hereafter "FTS tables"). The full-text index allows the user to
efficiently query the database for all rows that contain one or more instances of a
specified word (hereafter a "token"), even if the table contains many large documents.
Short introduction to FTS
The first full-text search modules for SQLite were called "FTS1" and "FTS2" and are now
obsolete. The latest recommended module is "FTS4"; however the former module "FTS3" is
still supporter. Detailed documentation for both "FTS4" and "FTS3" can be found at
<http://www.sqlite.org/fts3.html>, including explanations about the differences between
these two versions.
Here is a very short example of using FTS :
$dbh->do(<<"") or die DBI::errstr;
CREATE VIRTUAL TABLE fts_example USING fts4(content)
my $sth = $dbh->prepare("INSERT INTO fts_example(content) VALUES (?))");
$sth->execute($_) foreach @docs_to_insert;
my $results = $dbh->selectall_arrayref(<<"");
SELECT docid, snippet(content) FROM fts_example WHERE content MATCH 'foo'
The key points in this example are :
o The syntax for creating FTS tables is
CREATE VIRTUAL TABLE <table_name> USING fts4(<columns>)
where "<columns>" is a list of column names. Columns may be typed, but the type
information is ignored. If no columns are specified, the default is a single column
named "content". In addition, FTS tables have an implicit column called "docid" (or
also "rowid") for numbering the stored documents.
o Statements for inserting, updating or deleting records use the same syntax as for
regular SQLite tables.
o Full-text searches are specified with the "MATCH" operator, and an operand which may
be a single word, a word prefix ending with '*', a list of words, a "phrase query" in
double quotes, or a boolean combination of the above.
o The builtin function "snippet(...)" builds a formatted excerpt of the document text,
where the words pertaining to the query are highlighted.
There are many more details to building and searching FTS tables, so we strongly invite
you to read the full documentation at <http://www.sqlite.org/fts3.html>.
Incompatible change : starting from version 1.31, "DBD::SQLite" uses the new, recommended
"Enhanced Query Syntax" for binary set operators (AND, OR, NOT, possibly nested with
parenthesis). Previous versions of "DBD::SQLite" used the "Standard Query Syntax" (see
<http://www.sqlite.org/fts3.html#section_3_2>). Unfortunately this is a compilation
switch, so it cannot be tuned at runtime; however, since FTS3 was never advertised in
versions prior to 1.31, the change should be invisible to the vast majority of
"DBD::SQLite" users. If, however, there are any applications that nevertheless were built
using the "Standard Query" syntax, they have to be migrated, because the precedence of the
"OR" operator has changed. Conversion from old to new syntax can be automated through
DBD::SQLite::FTS3Transitional, published in a separate distribution.
Tokenizers
The behaviour of full-text indexes strongly depends on how documents are split into
tokens; therefore FTS table declarations can explicitly specify how to perform
tokenization:
CREATE ... USING fts4(<columns>, tokenize=<tokenizer>)
where "<tokenizer>" is a sequence of space-separated words that triggers a specific
tokenizer. Tokenizers can be SQLite builtins, written in C code, or Perl tokenizers. Both
are as explained below.
SQLite builtin tokenizers
SQLite comes with three builtin tokenizers :
simple
Under the simple tokenizer, a term is a contiguous sequence of eligible characters,
where eligible characters are all alphanumeric characters, the "_" character, and all
characters with UTF codepoints greater than or equal to 128. All other characters are
discarded when splitting a document into terms. They serve only to separate adjacent
terms.
All uppercase characters within the ASCII range (UTF codepoints less than 128), are
transformed to their lowercase equivalents as part of the tokenization process. Thus,
full-text queries are case-insensitive when using the simple tokenizer.
porter
The porter tokenizer uses the same rules to separate the input document into terms,
but as well as folding all terms to lower case it uses the Porter Stemming algorithm
to reduce related English language words to a common root.
icu If SQLite is compiled with the SQLITE_ENABLE_ICU pre-processor symbol defined, then
there exists a built-in tokenizer named "icu" implemented using the ICU library, and
taking an ICU locale identifier as argument (such as "tr_TR" for Turkish as used in
Turkey, or "en_AU" for English as used in Australia). For example:
CREATE VIRTUAL TABLE thai_text USING fts4(text, tokenize=icu th_TH)
The ICU tokenizer implementation is very simple. It splits the input text according to
the ICU rules for finding word boundaries and discards any tokens that consist
entirely of white-space. This may be suitable for some applications in some locales,
but not all. If more complex processing is required, for example to implement stemming
or discard punctuation, use the perl tokenizer as explained below.
Perl tokenizers
In addition to the builtin SQLite tokenizers, "DBD::SQLite" implements a perl tokenizer,
that can hook to any tokenizing algorithm written in Perl. This is specified as follows :
CREATE ... USING fts4(<columns>, tokenize=perl '<perl_function>')
where "<perl_function>" is a fully qualified Perl function name (i.e. prefixed by the name
of the package in which that function is declared). So for example if the function is
"my_func" in the main program, write
CREATE ... USING fts4(<columns>, tokenize=perl 'main::my_func')
That function should return a code reference that takes a string as single argument, and
returns an iterator (another function), which returns a tuple "($term, $len, $start, $end,
$index)" for each term. Here is a simple example that tokenizes on words according to the
current perl locale
sub locale_tokenizer {
return sub {
my $string = shift;
use locale;
my $regex = qr/\w+/;
my $term_index = 0;
return sub { # closure
$string =~ /$regex/g or return; # either match, or no more token
my ($start, $end) = ($-[0], $+[0]);
my $len = $end-$start;
my $term = substr($string, $start, $len);
return ($term, $len, $start, $end, $term_index++);
}
};
}
There must be three levels of subs, in a kind of "Russian dolls" structure, because :
o the external, named sub is called whenever accessing a FTS table with that tokenizer
o the inner, anonymous sub is called whenever a new string needs to be tokenized (either
for inserting new text into the table, or for analyzing a query).
o the innermost, anonymous sub is called repeatedly for retrieving all terms within that
string.
Instead of writing tokenizers by hand, you can grab one of those already implemented in
the Search::Tokenizer module. For example, if you want ignore differences between accented
characters, you can write :
use Search::Tokenizer;
$dbh->do(<<"") or die DBI::errstr;
CREATE ... USING fts4(<columns>,
tokenize=perl 'Search::Tokenizer::unaccent')
Alternatively, you can use "new" in Search::Tokenizer to build your own tokenizer.
Incomplete handling of utf8 characters
The current FTS implementation in SQLite is far from complete with respect to utf8
handling : in particular, variable-length characters are not treated correctly by the
builtin functions "offsets()" and "snippet()".
Database space for FTS
By default, FTS stores a complete copy of the indexed documents, together with the
fulltext index. On a large collection of documents, this can consume quite a lot of disk
space. However, FTS has some options for compressing the documents, or even for not
storing them at all -- see <http://www.sqlite.org/fts3.html#fts4_options>.
R* TREE SUPPORT
The RTREE extension module within SQLite adds support for creating a R-Tree, a special
index for range and multidimensional queries. This allows users to create tables that can
be loaded with (as an example) geospatial data such as latitude/longitude coordinates for
buildings within a city :
CREATE VIRTUAL TABLE city_buildings USING rtree(
id, -- Integer primary key
minLong, maxLong, -- Minimum and maximum longitude
minLat, maxLat -- Minimum and maximum latitude
);
then query which buildings overlap or are contained within a specified region:
# IDs that are contained within query coordinates
my $contained_sql = <<"";
SELECT id FROM try_rtree
WHERE minLong >= ? AND maxLong <= ?
AND minLat >= ? AND maxLat <= ?
# ... and those that overlap query coordinates
my $overlap_sql = <<"";
SELECT id FROM try_rtree
WHERE maxLong >= ? AND minLong <= ?
AND maxLat >= ? AND minLat <= ?
my $contained = $dbh->selectcol_arrayref($contained_sql,undef,
$minLong, $maxLong, $minLat, $maxLat);
my $overlapping = $dbh->selectcol_arrayref($overlap_sql,undef,
$minLong, $maxLong, $minLat, $maxLat);
For more detail, please see the SQLite R-Tree page (<http://www.sqlite.org/rtree.html>).
Note that custom R-Tree queries using callbacks, as mentioned in the prior link, have not
been implemented yet.
FOR DBD::SQLITE EXTENSION AUTHORS
Since 1.30_01, you can retrieve the bundled sqlite C source and/or header like this:
use File::ShareDir 'dist_dir';
use File::Spec::Functions 'catfile';
# the whole sqlite3.h header
my $sqlite3_h = catfile(dist_dir('DBD-SQLite'), 'sqlite3.h');
# or only a particular header, amalgamated in sqlite3.c
my $what_i_want = 'parse.h';
my $sqlite3_c = catfile(dist_dir('DBD-SQLite'), 'sqlite3.c');
open my $fh, '<', $sqlite3_c or die $!;
my $code = do { local $/; <$fh> };
my ($parse_h) = $code =~ m{(
/\*+[ ]Begin[ ]file[ ]$what_i_want[ ]\*+
.+?
/\*+[ ]End[ ]of[ ]$what_i_want[ ]\*+/
)}sx;
open my $out, '>', $what_i_want or die $!;
print $out $parse_h;
close $out;
You usually want to use this in your extension's "Makefile.PL", and you may want to add
DBD::SQLite to your extension's "CONFIGURE_REQUIRES" to ensure your extension users use
the same C source/header they use to build DBD::SQLite itself (instead of the ones
installed in their system).
TO DO
The following items remain to be done.
Leak Detection
Implement one or more leak detection tests that only run during AUTOMATED_TESTING and
RELEASE_TESTING and validate that none of the C code we work with leaks.
Stream API for Blobs
Reading/writing into blobs using "sqlite2_blob_open" / "sqlite2_blob_close".
Flags for sqlite3_open_v2
Support the full API of sqlite3_open_v2 (flags for opening the file).
Support for custom callbacks for R-Tree queries
Custom queries of a R-Tree index using a callback are possible with the SQLite C API
(<http://www.sqlite.org/rtree.html>), so one could potentially use a callback that
narrowed the result set down based on a specific need, such as querying for overlapping
circles.
SUPPORT
Bugs should be reported via the CPAN bug tracker at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=DBD-SQLite>
Note that bugs of bundled sqlite library (i.e. bugs in "sqlite3.[ch]") should be reported
to the sqlite developers at sqlite.org via their bug tracker or via their mailing list.
AUTHORS
Matt Sergeant <matt AT sergeant.org>
Francis J. Lacoste <flacoste AT logreport.org>
Wolfgang Sourdeau <wolfgang AT logreport.org>
Adam Kennedy <adamk AT cpan.org>
Max Maischein <corion AT cpan.org>
Laurent Dami <dami AT cpan.org>
Kenichi Ishigaki <ishigaki AT cpan.org>
COPYRIGHT
The bundled SQLite code in this distribution is Public Domain.
DBD::SQLite is copyright 2002 - 2007 Matt Sergeant.
Some parts copyright 2008 Francis J. Lacoste.
Some parts copyright 2008 Wolfgang Sourdeau.
Some parts copyright 2008 - 2013 Adam Kennedy.
Some parts copyright 2009 - 2013 Kenichi Ishigaki.
Some parts derived from DBD::SQLite::Amalgamation copyright 2008 Audrey Tang.
This program is free software; you can redistribute it and/or modify it under the same
terms as Perl itself.
The full text of the license can be found in the LICENSE file included with this module.
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