UPDATE

Description

The UPDATE statement is used to modify the existing records in a table.

Syntax

Single-table Syntax

  1. UPDATE table_reference
  2.     SET assignment_list
  3.     [WHERE where_condition]
  4.     [ORDER BY ...]
  5.     [LIMIT row_count]

Explanations

  • The UPDATE statement updates columns of existing rows in the named table with new values.
  • The SET clause indicates which columns to modify and the values they should be given. Each value can be given as an expression, or the keyword DEFAULT to set a column explicitly to its default value.
  • The WHERE clause, if given, specifies the conditions that identify which rows to update. With no WHERE clause, all rows are updated.
  • If the ORDER BY clause is specified, the rows are updated in the order that is specified.
  • The LIMIT clause places a limit on the number of rows that can be updated.

Examples

  • Single-table Examples
  1. CREATE TABLE t1 (a bigint(3), b bigint(5) primary key);
  2. insert INTO t1 VALUES (1,1),(1,2);
  3. update t1 set a=2 where a=1 limit 1;
  5. mysql> select * from t1;
  6. +------+------+
  7. | a    | b    |
  8. +------+------+
  9. |    2 |    1 |
  10. |    1 |    2 |
  11. +------+------+
  • Multiple-table Examples
  1. drop table if exists t1;
  2. create table t1 (a int);
  3. insert into t1 values(1), (2), (4);
  4. drop table if exists t2;
  5. create table t2 (b int);
  6. insert into t2 values(1), (2), (3);
  7. update t1, t2 set a = 1, b =2;
  9. mysql> select * from t1;
  10. +------+
  11. | a    |
  12. +------+
  13. |    1 |
  14. |    1 |
  15. |    1 |
  16. +------+
  18. update t1, t2 set a = null, b =null;
  20. mysql> select * from t2;
  21. +------+
  22. | b    |
  23. +------+
  24. | NULL |
  25. | NULL |
  26. | NULL |
  27. +------+
  28. mysql> select * from t1;
  29. +------+
  30. | a    |
  31. +------+
  32. | NULL |
  33. | NULL |
  34. | NULL |
  35. +------+

Multiple-table join Syntax is also supported.

  1. drop table if exists t1;
  2. drop table if exists t2;
  3. create table t1 (a int, b int, c int);
  4. insert into t1 values(1, 2, 3), (4, 5, 6), (7, 8, 9);
  5. create table t2 (a int, b int, c int);
  6. insert into t2 values(1, 2, 3), (4, 5, 6), (7, 8, 9);
  7. update t1 join t2 on t1.a = t2.a set t1.b = 222, t1.c = 333, t2.b = 222, t2.c = 333;
  9. mysql> select * from t1;
  10. +------+------+------+
  11. | a    | b    | c    |
  12. +------+------+------+
  13. |    1 |  222 |  333 |
  14. |    4 |  222 |  333 |
  15. |    7 |  222 |  333 |
  16. +------+------+------+
  18. mysql> with t11 as (select * from (select * from t1) as t22) update t11 join t2 on t11.a = t2.a set t2.b = 666;
  20. mysql> select * from t2;
  21. +------+------+------+
  22. | a    | b    | c    |
  23. +------+------+------+
  24. |    1 |  666 |  333 |
  25. |    4 |  666 |  333 |
  26. |    7 |  666 |  333 |
  27. +------+------+------+
  28. 3 rows in set (0.00 sec)