# 创建表 创建触发器
mysql> CREATE TABLE account (acct_num INT, amount DECIMAL(10,2));
Query OK, 0 rows affected (0.03 sec)
mysql> INSERT INTO account VALUES(137,14.98),(141,1937.50),(97,-100.00);
mysql> delimiter //
mysql> CREATE TRIGGER upd_check BEFORE UPDATE ON account
FOR EACH ROW
BEGIN
IF NEW.amount < 0 THEN
SET NEW.amount = 0;
ELSEIF NEW.amount > 100 THEN
SET NEW.amount = 100;
END IF;
END;//
mysql> delimiter ;
# 验证触发器作用
mysql> select * from account;
+
| acct_num | amount |
+
| 137 | 14.98 |
| 141 | 1937.50 |
| 97 | -100.00 |
+
3 rows in set (0.00 sec)
mysql> update account set amount = 114.98 where acct_num = 137;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select * from account;
+
| acct_num | amount |
+
| 137 | 100.00 |
| 141 | 1937.50 |
| 97 | -100.00 |
+
3 rows in set (0.00 sec)
# 查看触发器
mysql> show triggers;
# 删除触发器
mysql> drop trigger if exists upd_check;
# 查看数据库实例中所有触发器
SELECT
a.TRIGGER_SCHEMA,
a.TRIGGER_NAME,
a.ACTION_TIMING,
a.EVENT_OBJECT_TABLE,
a.EVENT_MANIPULATION
FROM
information_schema.`TRIGGERS` a
WHERE
a.TRIGGER_SCHEMA NOT IN ( 'information_schema', 'performance_schema', 'mysql', 'sys' );
delimiter // 设置MySQL执行结束标志，默认为;
