Updates 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> ]
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.
If the WHERE CURRENT OF
clause is specified, the row that is updated is the one most recently fetched from the specified cursor.
You must have the UPDATE
privilege on the table to update it, as well as the SELECT
privilege to any table whose values are read in the expressions or condition.
Outputs
On successful completion, an UPDATE
command returns a command tag of the form:
UPDATE <count>
where count is the number of rows updated. If count is 0, no rows matched the condition (this is not considered an error).
UPDATE foo AS f
, the remainder of the
UPDATE
statement must refer to this table as
f
not
foo
.
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 fromlist, unless you intend a self-join (in which case it must appear with an alias in the fromlist).
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 the cursor. The cursor must be a simple (non-join, non-aggregate) query on the UPDATE
command target table. See DECLARE for more information about creating cursors.
WHERE CURRENT OF
cannot be specified together with a Boolean condition.
The UPDATE...WHERE CURRENT OF
statement can only be executed on the server, for example in an interactive psql session or a script. Language extensions such as PL/pgSQL do not have support for updatable cursors.
UPDATE
command after each row is updated. The expression may use any column names of the table or table(s) listed in
FROM
. Write
*
to return all columns.
SET
is not allowed on the Greenplum distribution key columns of a table.
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 should not 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.
Executing UPDATE
and DELETE
commands directly on a specific partition (child table) of a partitioned table is not supported. Instead, execute these commands on the root partitioned table, the table created with the CREATE TABLE
command.
For a partitioned table, all the child tables are locked during the UPDATE
operation.
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 = '2016-07-03';
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 = '2016-07-03';
Increment the sales count of the salesperson who manages the account for Acme Corporation, using the FROM
clause syntax (assuming both tables being joined are distributed in Greenplum Database on the id
column):
UPDATE employees SET sales_count = sales_count + 1 FROM
accounts
WHERE accounts.name = 'Acme Corporation'
AND employees.id = accounts.id;
Perform the same operation, using a sub-select in the WHERE
clause:
UPDATE employees SET sales_count = sales_count + 1 WHERE id =
(SELECT id 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;
This command conforms to the SQL standard, except that the FROM
clause is a Greenplum Database extension.
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 Greenplum Database interprets FROM
. Be careful when porting applications that use this extension.
DECLARE, DELETE, SELECT, INSERT
Parent topic: SQL Command Reference