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 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, 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.

       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 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 cur-
	      sor. 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 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 val-
       ues 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 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 ta-
       ble(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 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 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 extension.

SQL - Language Statements					    2010-05-14								 UPDATE(7)