MySql 游标和触发器概念及使用详解

DECLARE cursor_name CURSOR FOR select_statement;

DECLARE cur_score CURSOR FOR
	SELECT stu_id,grade FROM score;

OPEN 游标名称
-- 例如
open cur_score;

FETCH cursor_name INTO var_name [, var_name] ...
FETCH cur_score INTO stu_id, grade ;

CLOSE 游标名称;
CLOSE cur_score;

CREATE PROCEDURE PROC_CURSOR(IN LIMIT_TOTAL_GRADE INT, OUT TOTAL_COUNT INT )
BEGIN
# 声明相关的变量
DECLARE SUM_GRADE INT DEFAULT 0; # 累加的总成绩
DECLARE CURSOR_GRADE INT DEFAULT 0; # 记录某条成绩
DECLARE SCORE_COUNT INT DEFAULT 0; # 记录累加的记录数
# 定义游标
DECLARE SCORE_CURSOR CURSOR FOR SELECT GRADE FROM SCORE ORDER BY GRADE ;
# 打开游标
OPEN SCORE_CURSOR;
# 使用游标
REPEAT
FETCH SCORE_CURSOR INTO CURSOR_GRADE; # 从游标中获取一条数据
SET SUM_GRADE = SUM_GRADE + CURSOR_GRADE; # 成绩累加
SET SCORE_COUNT = SCORE_COUNT + 1; # 记录累加的次数
UNTIL SUM_GRADE > LIMIT_TOTAL_GRADE # 退出条件
END REPEAT ;
# 复制OUT参数
SET TOTAL_COUNT = SCORE_COUNT;
# 关闭游标
CLOSE SCORE_CURSOR;
END;
DROP PROCEDURE PROC_CURSOR
# 调用存储过程
SET @s_count = 0;
CALL PROC_CURSOR(400,@s_count) ;
SELECT @s_count;

CREATE TRIGGER 触发器名称
{BEFORE|AFTER} {INSERT|UPDATE|DELETE} ON 表名
FOR EACH ROW
触发器执行的语句块;

CREATE TABLE test_trigger (
id INT PRIMARY KEY AUTO_INCREMENT,
t_note VARCHAR(30) );
CREATE TABLE test_trigger_log (
id INT PRIMARY KEY AUTO_INCREMENT,
t_log VARCHAR(30)
);

CREATE TRIGGER BEFORE_INSERT
BEFORE INSERT ON TEST_TRIGGER
FOR EACH ROW
BEGIN
INSERT INTO TEST_TRIGGER_LOG(T_LOG)VALUES('BEFORE_INSERT ....') ;
END;

insert into test_trigger(t_note)values('test data');

select * from test_trigger_log;

SHOW TRIGGERS\G

SHOW CREATE TRIGGER 触发器名

SELECT * FROM information_schema.TRIGGERS;

DROP TRIGGER IF EXISTS 触发器名称;