浅谈mysql双层not exists查询执行流程

DROP TABLE IF EXISTS `t_staff`;
CREATE TABLE `t_staff` (
  `id` int(11) NOT NULL,
  `name` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='人员表';
DROP TABLE IF EXISTS `t_major`;
CREATE TABLE `t_major` (
  `id` int(11) NOT NULL,
  `staff_id` int(11) NOT NULL,
  `name` varchar(255) NOT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='技能表';
INSERT INTO `t_staff` VALUES ('1', '张辽');
INSERT INTO `t_staff` VALUES ('2', '赵云');
INSERT INTO `t_staff` VALUES ('3', '夏侯渊');
INSERT INTO `t_major` VALUES ('1', '2', '大鹏展翅');
INSERT INTO `t_major` VALUES ('2', '2', '无敌风火轮');
INSERT INTO `t_major` VALUES ('3', '3', '横扫千军');

SELECT * FROM t_student_course WHERE TRUE;     --  能查出数据
SELECT * FROM t_student_course WHERE FALSE;    -- 不能查出数据

SELECT * FROM t_staff where id in (SELECT staff_id FROM t_major);
SELECT * FROM t_staff where EXISTS (
    SELECT 1 from t_major where t_staff.id = t_major.staff_id
);
-- 赵云、夏侯渊

SELECT * FROM t_staff where id not in (SELECT staff_id FROM t_major);
SELECT * FROM t_staff where NOT EXISTS (
    SELECT 1 from t_major where t_staff.id = t_major.staff_id
);
-- 张辽

DROP TABLE IF EXISTS `t_student`;
CREATE TABLE `t_student` (
  `id` int(11) NOT NULL,
  `name` varchar(255) DEFAULT NULL COMMENT '姓名',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
DROP TABLE IF EXISTS `t_course`;
CREATE TABLE `t_course` (
  `id` int(11) NOT NULL,
  `name` varchar(255) DEFAULT NULL COMMENT '课程名称',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
DROP TABLE IF EXISTS `t_student_course`;
CREATE TABLE `t_student_course` (
  `id` int(11) NOT NULL,
  `sid` varchar(255) NOT NULL,
  `cid` varchar(255) NOT NULL,
  `score` decimal(10,0) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
INSERT INTO `t_student` VALUES (1, '赵子龙');
INSERT INTO `t_student` VALUES (2, '关羽');
INSERT INTO `t_student` VALUES (3, '张飞');
INSERT INTO `t_student` VALUES (4, '黄忠');
INSERT INTO `t_student` VALUES (5, '马超');
INSERT INTO `t_course` VALUES (1, '语文');
INSERT INTO `t_course` VALUES (2, '数学');
INSERT INTO `t_course` VALUES (3, '英语');
INSERT INTO `t_student_course` VALUES (1, 1, 1, 95);
INSERT INTO `t_student_course` VALUES (2, 1, 2, 99);
INSERT INTO `t_student_course` VALUES (3, 1, 3, 100);
INSERT INTO `t_student_course` VALUES (4, 2, 1, 99);
INSERT INTO `t_student_course` VALUES (5, 2, 2, 100);
INSERT INTO `t_student_course` VALUES (6, 3, 2, 100);
INSERT INTO `t_student_course` VALUES (7, 3, 3, 95);
INSERT INTO `t_student_course` VALUES (8, 4, 1, 100);

SELECT name from t_student where id in(
    SELECT sid FROM t_student_course GROUP BY sid 
        HAVING (count(sid)) = (SELECT count(*) from t_course)
)  -- 记录一般写法
SELECT name from t_student s where NOT EXISTS (
    SELECT 1 from t_course c where NOT EXISTS (
        SELECT 1 from t_student_course sc 
            where sc.sid = s.id and sc.cid = c.id
    )
)
-- 赵子龙

let a1 = SELECT 1 from t_student_course sc 
            where sc.sid = s.id and sc.cid = c.id
let b1 = SELECT 1 FROM t_role WHERE NOT EXISTS (a1)
let c1 = SELECT * FROM t_account WHERE NOT EXISTS (b1);

SELECT name from t_student s where EXISTS (
    SELECT 1 from t_course c where EXISTS (
        SELECT 1 from t_student_course sc 
              where sc.sid = s.id and sc.cid = c.id
    )
)
-- 赵子龙、关羽、张飞、黄忠

SELECT name from t_student s where EXISTS (
    SELECT 1 from t_course c where NOT EXISTS (
        SELECT 1 from t_student_course sc 
            where sc.sid = s.id and sc.cid = c.id
    )
)
-- 关羽、张飞、黄忠、马超

SELECT name FROM t_student s where NOT EXISTS (
    SELECT 1 from t_course c where EXISTS (
        SELECT 1 from t_student_course sc 
            where sc.sid = s.id and sc.cid = c.id
    )
)
-- 马超

select * from t_student s where id != 2 and NOT EXISTS ( 
    select 1 from t_student_course sc where sid = 2 and NOT EXISTS ( 
        select 1 from t_student_course sc2 
            where sc2.cid = sc.cid and sc2.sid = s.id 
    ) 
)
-- 赵子龙

SELECT * FROM t_student_course sc 
    where sc.score = (SELECT max(score) FROM t_student_course sc2 
                        where sc2.cid = sc.cid)
SELECT * FROM t_student_course sc where NOT EXISTS (
    SELECT 1 FROM t_student_course sc2 
        where sc2.cid = sc.cid and sc2.score > sc.score
)