Provided by: postgresql-client-8.4_8.4.11-1_amd64 bug


       UPDATE - update rows of a table


       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 ] [, ...] ]


       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.


       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

              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 [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).

              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 [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 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 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.

       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.