DEFAULT

声明

DEFAULT(col_name)

说明

返回表列的默认值，如果指定的列没有默认值，则会返回 NULL。

示例

CREATE TABLE t1 (id int,i int DEFAULT 1);
Query OK, 0 rows affected
INSERT INTO t1 VALUES (1,3);
Query OK, 1 row affected
UPDATE t1 SET i = DEFAULT(i)+1 WHERE id < 100;
Query OK, 1 row affected
Rows matched: 1  Changed: 1  Warnings: 0
SELECT * FROM t;
+------+------+
| id   | i    |
+------+------+
|    1 |    2 |
+------+------+
1 row in set (0.001 sec)

CREATE TABLE t2 (id int,i int);
Query OK, 0 rows affected
INSERT INTO t2 VALUES (1,3);
Query OK, 1 row affected
UPDATE t2 SET i = DEFAULT(i)+1 WHERE id < 100;
SELECT * FROM t2;
+------+------+
| id   | i    |
+------+------+
|    1 | NULL |
+------+------+
1 row in set (0.001 sec)