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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 mentioned in the SET clause; columns not explic-
itly 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 to update it, as well as the SELECT privi-
lege 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 provided, it completely
hides the actual name of the table. For example, given UPDATE foo AS f, the remain-
der 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 specifi-
cation 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 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 cur-
rently 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()
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On Apache
Under GNU General Public License
2012-05-26 04:34 @38.107.179.236 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)