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UPDATE(7)                        SQL Commands                        UPDATE(7)



NAME
       UPDATE - update rows of a table


SYNOPSIS
       UPDATE [ ONLY ] table [ * ] [ [ AS ] alias ]
           SET { column = { expression | DEFAULT } |
                 ( column [, ...] ) = ( { expression | DEFAULT } [, ...] ) } [, ...]
           [ FROM fromlist ]
           [ WHERE condition | WHERE CURRENT OF cursor_name ]
           [ RETURNING * | output_expression [ [ AS ] output_name ] [, ...] ]


DESCRIPTION
       UPDATE  changes the values of the specified columns in all rows that satisfy the condition. Only the columns to
       be modified need be mentioned in the SET clause; columns not explicitly modified retain their previous  values.

       There  are  two  ways to modify a table using information contained in other tables in the database: using sub-
       selects, or specifying additional tables in the FROM clause. Which technique is more appropriate depends on the
       specific circumstances.

       The  optional RETURNING clause causes UPDATE to compute and return value(s) based on each row actually updated.
       Any expression using the table's columns, and/or columns of other tables mentioned in FROM,  can  be  computed.
       The new (post-update) values of the table's columns are used.  The syntax of the RETURNING list is identical to
       that of the output list of SELECT.

       You must have the UPDATE privilege on the table, or at least on the column(s) that are listed  to  be  updated.
       You must also have the SELECT privilege on any column whose values are read in the expressions or condition.

PARAMETERS
       table  The  name  (optionally  schema-qualified) of the table to update.  If ONLY is specified before the table
              name, matching rows are updated in the named table only. If ONLY is not  specified,  matching  rows  are
              also updated in any tables inheriting from the named table. Optionally, * can be specified after the ta-
              ble name to explicitly indicate that descendant tables are included.

       alias  A substitute name for the target table. When an alias is provided, it completely hides the  actual  name
              of  the  table.  For example, given UPDATE foo AS f, the remainder of the UPDATE statement must refer to
              this table as f not foo.

       column The name of a column in table.  The column name can be qualified with a  subfield  name  or  array  sub-
              script,  if  needed. Do not include the table's name in the specification of a target column -- for exam-
              ple, UPDATE tab SET tab.col = 1 is invalid.

       expression
              An expression to assign to the column. The expression can use the old values of this and  other  columns
              in the table.

       DEFAULT
              Set  the  column  to  its  default  value (which will be NULL if no specific default expression has been
              assigned to it).

       fromlist
              A list of table expressions, allowing columns from other tables to appear in the WHERE condition and the
              update  expressions.  This  is  similar  to  the list of tables that can be specified in the FROM Clause
              [select(7)] of a SELECT statement. Note that the target table must not appear in  the  fromlist,  unless
              you intend a self-join (in which case it must appear with an alias in the fromlist).

       condition
              An  expression  that  returns a value of type boolean.  Only rows for which this expression returns true
              will be updated.

       cursor_name
              The name of the cursor to use in a WHERE CURRENT OF condition. The row to be updated  is  the  one  most
              recently fetched from this cursor. The cursor must be a non-grouping query on the UPDATE's target table.
              Note that WHERE CURRENT  OF  cannot  be  specified  together  with  a  Boolean  condition.  See  DECLARE
              [declare(7)] for more information about using cursors with WHERE CURRENT OF.

       output_expression
              An  expression  to be computed and returned by the UPDATE command after each row is updated. The expres-
              sion can use any column names of the table or table(s) listed in FROM.  Write * to return all columns.

       output_name
              A name to use for a returned column.

OUTPUTS
       On successful completion, an UPDATE command returns a command tag of the form

       UPDATE count

       The count is the number of rows updated. If count is 0, no rows matched the condition (this is  not  considered
       an error).

       If  the  UPDATE  command  contains a RETURNING clause, the result will be similar to that of a SELECT statement
       containing the columns and values defined in the RETURNING list, computed over the row(s) updated by  the  com-
       mand.

NOTES
       When  a  FROM clause is present, what essentially happens is that the target table is joined to the tables men-
       tioned in the fromlist, and each output row of the join represents an update operation for  the  target  table.
       When using FROM you should ensure that the join produces at most one output row for each row to be modified. In
       other words, a target row shouldn't join to more than one row from the other table(s). If it  does,  then  only
       one  of  the  join  rows  will be used to update the target row, but which one will be used is not readily pre-
       dictable.

       Because of this indeterminacy, referencing other tables only within sub-selects is safer, though  often  harder
       to read and slower than using a join.

EXAMPLES
       Change the word Drama to Dramatic in the column kind of the table films:

       UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';


       Adjust temperature entries and reset precipitation to its default value in one row of the table weather:

       UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
         WHERE city = 'San Francisco' AND date = '2003-07-03';


       Perform the same operation and return the updated entries:

       UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
         WHERE city = 'San Francisco' AND date = '2003-07-03'
         RETURNING temp_lo, temp_hi, prcp;


       Use the alternative column-list syntax to do the same update:

       UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT)
         WHERE city = 'San Francisco' AND date = '2003-07-03';


       Increment  the  sales  count  of  the  salesperson who manages the account for Acme Corporation, using the FROM
       clause syntax:

       UPDATE employees SET sales_count = sales_count + 1 FROM accounts
         WHERE accounts.name = 'Acme Corporation'
         AND employees.id = accounts.sales_person;


       Perform the same operation, using a sub-select in the WHERE clause:

       UPDATE employees SET sales_count = sales_count + 1 WHERE id =
         (SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');


       Attempt to insert a new stock item along with the quantity of stock. If the item already exists, instead update
       the stock count of the existing item. To do this without failing the entire transaction, use savepoints:

       BEGIN;
       -- other operations
       SAVEPOINT sp1;
       INSERT INTO wines VALUES('Chateau Lafite 2003', '24');
       -- Assume the above fails because of a unique key violation,
       -- so now we issue these commands:
       ROLLBACK TO sp1;
       UPDATE wines SET stock = stock + 24 WHERE winename = 'Chateau Lafite 2003';
       -- continue with other operations, and eventually
       COMMIT;


       Change the kind column of the table films in the row on which the cursor c_films is currently positioned:

       UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;


COMPATIBILITY
       This  command  conforms  to  the SQL standard, except that the FROM and RETURNING clauses are PostgreSQL exten-
       sions.

       According to the standard, the column-list syntax should allow a list of columns to be assigned from  a  single
       row-valued expression, such as a sub-select:

       UPDATE accounts SET (contact_last_name, contact_first_name) =
           (SELECT last_name, first_name FROM salesmen
            WHERE salesmen.id = accounts.sales_id);

       This is not currently implemented -- the source must be a list of independent expressions.

       Some other database systems offer a FROM option in which the target table is supposed to be listed again within
       FROM.  That is not how PostgreSQL interprets FROM. Be careful when porting applications that  use  this  exten-
       sion.



SQL - Language Statements         2014-02-17                         UPDATE(7)