mysql存储过程

定义变量

SET @username = ‘yly’;

定义函数

DROP FUNCTION IF EXISTS select_by;
DELIMITER //
CREATE FUNCTION select_by(INT(10) user_id)
RETURNS VARCHAR(25)
	DETERMINISTIC # 是否具有确定性->多次执行结果是否相同
	CONTAINS SQL # 是否包含sql
	READS SQL DATA # 只是读取sql数据，不做修改
	# 不加上面这些限定会报错

BEGIN
        RETURN (SELECT username FROM sys_user su WHERE su.user_id=user_id);
END //
DELIMITER ;

调用函数

SELECT select_by(2022);

定义存储过程

-- in
DROP PROCEDURE IF EXISTS select_user_by_username;
DELIMITER $$
CREATE PROCEDURE select_user_by_username(IN username VARCHAR(20)) -- IN 入参 OUT 出参 INOUT 都行
BEGIN
	SELECT * FROM sys_user su
	WHERE su.username=username;
END $$
DELIMITER ;
-- out
DROP PROCEDURE IF EXISTS select_user_by_username;
DELIMITER $$
CREATE PROCEDURE select_user_by_username(IN username VARCHAR(20),OUT userdata VARCHAR(40)) -- IN 入参 OUT 出参 INOUT 都行
BEGIN
	SELECT su.username INTO userdata 
	FROM sys_user su
	WHERE su.username=username;
END $$
DELIMITER ;

调用存储过程

-- 1
CALL select_user_by_username('yly');
-- 2
SET @username = '';
CALL select_user_by_username('yly',@username);
SELECT @username;

查看存储过程

-- 1
-- 创建信息
SHOW CREATE PROCEDURE select_user_by_username;
SHOW CREATE FUNCTION select_by;

-- 状态信息
SHOW PROCEDURE STATUS LIKE '';
SHOW FUNCTION STATUS LIKE '';
--2 从information_schema.Routines表中查看存储过程和函数的信息
SELECT * FROM information_schema.Routines 
WHERE ROUTINE_NAME='select_user_by_username' AND ROUTINE_TYPE='PROCEDURE';
SELECT * FROM information_schema.Routines 
WHERE ROUTINE_NAME='select_by' AND ROUTINE_TYPE='FUNCTION';

-- 修改
ALTER PROCEDURE select_user_by_username
COMMENT '通过username查询用户';

-- 删除
DROP PROCEDURE IF EXISTS select_user_by_username;

## mysql变量

mysql系统变量

-- 全局 会话

-- 查看系统变量
SHOW GLOBAL VARIABLES LIKE 'admin_%';
SHOW SESSTION VARIABLES LIKE 'character_%';
-- 查看指定系统变量
SELECT @@global.max_connections;
-- 修改
SET @@global.max_connections = 124;
SET GLOBAL max_connections = 123;
-- 全局系统变量是针对于当前数据库实例有效, 一旦重启mysql服务,就会失效;

mysql用户变量

-- 定义变量
-- 1
SET @username = '';
SET @username := '';
-- 2
SELECT @username := FROM sys_user;
SELECT username INTO @username := FROM sys_user;
-- 使用
SELECT @username;
-- 定义局部变量
-- 局部变量 使用DECLARE声明
-- 只能在 PROCEDURE, FUNCTION中使用;
-- BEGIN 首行

-- 声明格式
DECLARE username VARCHAR(30) '';
DELIMITER $$
CREATE PROCEDURE `test_var`()
BEGIN
  DECLARE username VARCHAR(20); -- 不指定则为空
  SELECT username INTO username FROM sys_user;
  SELECT username;
END;
$$
DELIMITER ;

定义错误与处理程序

定义错误条件

DECLARE '' /*error*/ CONDITION FOR ''/*error_code*/; 
DECLARE Field_Not_Be_NULL CONDITION FRO 1048;
DECLARE Field_Not_Be_NULL CONDITION FRO SQLSTATE '1048';

定义处理程序

DECLARE EXIT/**/ HANDLER FRO Field_Not_Be_NULL SET @INFO = 'ERROR';

if

-- IF(a,b,c) 相当于 a ? b : c
DROP PROCEDURE IF EXISTS test_var;
DELIMITER $$
BEGIN
  DECLARE username VARCHAR(20);
  SELECT su.username INTO username FROM sys_user su WHERE su.user_id=2022;

  IF username = 'yly'
    THEN SET username='';
    ELSEIF username='hello'
      THEN SET username='123456';
      ELSE SET username='hhhhh';
  END IF;
  SELECT username;
END;
$$
DELIMITER ;

case

DROP PROCEDURE IF EXISTS test_var;
DELIMITER $$
CREATE PROCEDURE `test_var`()
BEGIN
  DECLARE username VARCHAR(20);
  SELECT su.username INTO username FROM sys_user su WHERE su.user_id=2022;
  -- CASE username
   -- when 'yly3' THEN SET username='';
  -- When 'hello' THEN SET username='123456';
   -- Else SET username='else';
  -- end case;
 CASE 
  WHEN LENGTH(username)>4 THEN SET username='';
  WHEN LENGTH(username)>1 THEN SET username='123456'; 
  ELSE SET username='else';
  END CASE;
  SELECT username;
END;
$$
DELIMITER ;

loop while repeat

loop 感觉就像 for 一样

DROP PROCEDURE IF EXISTS test_loop;
DELIMITER $$
CREATE PROCEDURE `test_loop`()
BEGIN
  DECLARE username VARCHAR(20);
  DECLARE `count` INT(10) DEFAULT 0;
  SELECT su.username INTO username FROM sys_user su WHERE su.user_id=2022;
  loop_label:LOOP
    SET `count` = `count`+1;
    IF `count` >= 10 THEN LEAVE /*跳出循环*/ loop_label;
    END IF;
  END LOOP loop_label;
  SELECT username,`count`;	
END;
$$
DELIMITER ;

while 感觉就像 while 前面也可以加label

DROP PROCEDURE IF EXISTS test_while;
DELIMITER $$
CREATE PROCEDURE `test_while`()
BEGIN
  DECLARE username VARCHAR(20);
  DECLARE `count` INT(10) DEFAULT 0;
  SELECT su.username INTO username FROM sys_user su WHERE su.user_id=2022;
  WHILE `count` < 10 DO
    SET `count` = `count`+1;
  END WHILE
  SELECT username,`count`;	
END;
$$
DELIMITER ;

repeat 感觉就像 do while

DROP PROCEDURE IF EXISTS test_while;
DELIMITER $$
CREATE PROCEDURE `test_while`()
BEGIN
  DECLARE username VARCHAR(20);
  DECLARE `count` INT(10) DEFAULT 0;
  SELECT su.username INTO username FROM sys_user su WHERE su.user_id=2022;
  REPEAT  
    SET `count` = `count`+1;
    UNTIL `count` >= 10
  END REPEAT;
  SELECT username,`count`;	
END;
$$
DELIMITER ;

LEAVE 和 ITERATE 像 continue

-- LEAVE
DROP PROCEDURE IF EXISTS test_while;
DELIMITER $$
CREATE PROCEDURE `test_while`()
test:BEGIN
  DECLARE username VARCHAR(20);
  DECLARE `count` INT(10) DEFAULT 0;
  SELECT su.username INTO username FROM sys_user su WHERE su.user_id=2022;
  REPEAT  
    SET `count` = `count`+1;
    UNTIL `count` >= 10
  END REPEAT;
  LEAVE test; -- 到这就会停止
  SELECT username,`count`;	
END;
$$
DELIMITER ;
-- ITERATE
DROP PROCEDURE IF EXISTS test_loop;
DELIMITER $$
CREATE PROCEDURE `test_loop`()
BEGIN
  DECLARE username VARCHAR(20);
  DECLARE `count` INT(10) DEFAULT 0;
  SELECT su.username INTO username FROM sys_user su WHERE su.user_id=2022;
  loop_label:LOOP
    SELECT username,`count`;
    SET `count` = `count`+1;
    IF `count` >= 10 THEN LEAVE /*跳出循环*/ loop_label;
    END IF;
    IF `count` < 3 THEN SELECT 100; ITERATE loop_label;
    END IF;
    SET `count` = `count`+100;
  END LOOP loop_label;
  SELECT username,`count`;	
END;
$$
DELIMITER ;
CALL test_loop();

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