Provided by: postgresql-client-9.1_9.1.3-2_amd64 bug


       UPDATE - update rows of a table


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


       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.

       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 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.


           The WITH clause allows you to specify one or more subqueries that can be referenced by
           name in the UPDATE query. See Section 7.8, “WITH Queries (Common Table Expressions)”,
           in the documentation and SELECT(7) for details.

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

           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.

           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.

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

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

           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 of a SELECT statement. Note that the target table must
           not appear in the from_list, unless you intend a self-join (in which case it must
           appear with an alias in the from_list).

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

           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(7) for more information about using
           cursors with WHERE CURRENT OF.

           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.

           A name to use for a returned column.


       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.


       When a FROM clause is present, what essentially happens is that the target table is joined
       to the tables mentioned in the from_list, 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 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.


       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 = 'Acme Corporation'
             AND = 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:

           -- 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

       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;


       This command conforms to the SQL standard, except that the FROM and RETURNING clauses are
       PostgreSQL extensions, as is the ability to use WITH with UPDATE.

       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 = 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.