/* Void Main's man pages */
{ phpMan } else { main(); }
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 modi-
fied 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 circum-
stances.
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 ta-
ble. 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 ta-
ble.
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 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 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.
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 2011-09-22 UPDATE(7)
