UPDATE [ ONLY ] table SET column = { expression | DEFAULT } [, ...]
[ FROM fromlist ]
[ WHERE condition ]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.
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.
The name (optionally schema-qualified) of the table to update.
The name of a column in table. The column name can be qualified with a subfield name or array subscript, if needed.
An expression to assign to the column. The expression may 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; for example, an alias for the table name can be specified.
An expression that returns a value of type boolean. Only rows for which this expression returns true will be updated.
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).
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';
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 exists, update the stock count of the existing item. To do this, use savepoints.
BEGIN;
SAVEPOINT sp1;
INSERT INTO wines VALUES('Chateau Lafite 2003', '24');
-- Check for unique violation on name
ROLLBACK TO sp1;
UPDATE wines SET stock = stock + 24 WHERE winename='Chateau Lafite 2003';
COMMIT;