-- 測試子查詢
-- 測試由in引發的子查詢
select * from emp
where depid in (select id from dep);
select * from emp
where depid not in (select id from dep);
-- 由exists 引發的子查詢
select * from emp where exists (select depname from dep where id=10);
select * from emp where not exists (select depname from dep where id=1);
-- 學員stu
create table stu(
id tinyint unsigned auto_increment key,
username varchar(20) not null unique,
score tinyint unsigned not null
);insert stu(username,score) values('king',95),
('queen',75),
('zhangsan',69),
('lisi',78),
('wangwu',87),
('zhaoliu',88),
('tianqi',98),
('ceshi',99),
('tiancai',50);
-- 分數級別level
create table level(
id tinyint unsigned auto_increment key,
score tinyint unsigned comment '分數'
);insert level(score) values(90),(80),(70);
-- 查詢出成績優秀的學員
select score from level where id=1;
select id,username,score from stu
where score>=(select score from level where id=1);
-- 查詢出沒有得到評級的學員
select id,username,score from stu
where score<(select score from level where id=3);
-- 帶有any some all關鍵字的子查詢
select * from stu
where score>= any(select score from level);
select * from stu
where score>= some(select score from level);
select * from stu
where score>= all(select score from level);
select * from stu
where score< all(select score from level);
select * from stu
where score=any(select score from level);
select * from stu
where score!=all(select score from level);
-- 建立乙個user1表,id username
create table user1(
id int unsigned auto_increment key,
username varchar(20)
)select id,username from emp;
-- 將stu表中id=3的使用者名稱寫入到user1表中
insert user1(username) select username from stu where id=3;
-- 建立象user1一樣的表user2
create table user2 like user1;
insert user2(username) select username from stu;
-- 將stu表中的tiancai使用者名稱新增到user2表中
insert user2 set username=(select username from stu where id=5);
-- 去掉欄位的重複值
select distinct(username) from user2;
-- 將user1和user2資料合併到一起
--去重
select username from user1
union
select username from user2;
--不去重
select username from user1
union all
select username from user2;
MySQl學習筆記（子查詢）
修改資料表 新增單列 alter table tbl name add column col name column definition first after col name 省略first after col name將預設你所新增的列位於所有列的最後面 例 alter table user...
MySQL學習筆記 子查詢
子查詢是將乙個查詢語句巢狀在另乙個查詢語句中。內層查詢語句的查詢結果，可以作為外層查詢語句提供條件。insert into tbl name col name,select.create table if notexists tbl name create definition,select sta...
（MySQL筆記）MySQL子查詢
mysql的select語句中支援子查詢。子查詢是將乙個select語句的查詢結果作為中間結果，供另乙個select語句查詢呼叫，子查詢也叫做子選擇或者巢狀選擇。如 select studentno from select studentno,from student where age 18 as...