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UPDATE()                         SQL Commands                         UPDATE()

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  men-
       tioned  in the SET clause; columns not explicitly modified retain their
       previous values.

       By default, UPDATE will update rows in the specified table and all  its
       subtables. If you wish to only update the specific table mentioned, you
       must use the ONLY clause.

       There are two ways to modify a table  using  information  contained  in
       other  tables  in  the database: using sub-selects, or specifying addi-
       tional 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 to update it,  as  well
       as  the  SELECT  privilege  to  any  table whose values are read in the
       expressions or condition.

PARAMETERS
       table  The name (optionally schema-qualified) of the table to update.

       alias  A substitute name for the target table. When an  alias  is  pro-
              vided,  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  subscript,  if  needed.  Do  not
              include the table's name in the specification of a target column
              -- for example, 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 simple (non-join, non-aggregate)
              query on the UPDATE's target table.  Note that WHERE CURRENT  OF
              cannot be specified together with a Boolean condition.

       output_expression
              An  expression to be computed and returned by the UPDATE command
              after each row is updated. The expression  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
       command.

NOTES
       When  a  FROM  clause  is present, what essentially happens is that the
       target table is joined to the tables mentioned  in  the  fromlist,  and
       each output row of the join represents an update operation for the tar-
       get 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 tar-
       get 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 tar-
       get row, but which one will be used is not readily predictable.

       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 save-
       points:

       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  cur-
       sor 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 extensions.

       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 inde-
       pendent 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 extension.

SQL - Language Statements         2009-12-09                          UPDATE()

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