Update (SQL)

An SQL UPDATE statement changes the data of one or more records in a table. Either all the rows can be updated, or a subset may be chosen using a condition.

The UPDATE statement has the following form:

UPDATE table_name SET column_name = value [, column_name = value ...] [WHERE condition]

For the UPDATE to be successful, the user must have data manipulation privileges (UPDATE privilege) on the table or column, the updated value must not conflict with all the applicable constraints (such as primary keys, unique indexes, CHECK constraints, and NOT NULL constraints).

Examples

Set the value of column C1 in table T to 1, only if in those rows where the value of column C2 is "a".

 UPDATE T SET C1 = 1 WHERE C2 = 'a'

Increase value of column C1 by 1 if the value in column C2 is "a".

 UPDATE T SET C1 = C1 + 1 WHERE C2 = 'a'

Prepend the value in column C1 with the string "text" if the value in column C2 is "a".

 UPDATE T SET C1 = 'text' || C1 WHERE C2 = 'a'

Set the value of column C1 in table T1 to 2, only if the value of column C2 is found in the sub list of values in column C3 in table T2 having the column C4 equal to 0.

 UPDATE T1 
 SET    C1 = 2    
 WHERE  C2 in ( SELECT C3
                FROM   T2
                WHERE  C4 = 0)

You may also update multiple columns in a single update statement:

 UPDATE T SET C1 = 1, C2 = 2

Complex conditions are also possible:

 UPDATE T SET A = 1 WHERE C1 = 1 AND C2 = 2

The SQL:2003 standard does not support updates of a joined table. Therefore, the following method needs to be used. Note that the subselect in the SET clause must be a scalar subselect, i.e. it can return at most a single row.

UPDATE T1
SET    C1 = ( SELECT T2.C2
              FROM   T2
              WHERE  T1.ID = T2.ID )
WHERE  EXISTS ( SELECT 1
                FROM   T2
                WHERE  T1.ID = T2.ID )

References

• SQL UPDATE Statement