SQL -- select

user1; # 清空数据库 select * from user1; insert into user1 (id, username) values (0, ‘test0‘); insert into user1 (id, username) values (1, ‘test1‘); insert into user1 (id, username) values (2, ‘test2‘); insert into user1 (id, username) values (3, ‘test3‘); insert into user1 (id, username) values (4, ‘test4‘); insert into user1 (id, username) values (5, ‘test5‘); insert into user1 (id, username) values (6, ‘test6‘); insert into user1 (id, username) values (7, ‘test7‘); insert into user1 (id, username) values (8, ‘test8‘); insert into user1 (id, username) values (9, ‘test9‘); insert into user1 (id, username) values (100, ‘test100‘); insert into user1 (id, username) values (111, ‘test111‘); select * from user1;

select id, username from user1 where (id < 5) OR (id > 90);
select id, username from user1 where id between 5 and 90;            # [5, 90]
select id, username from user1 where id not between 5 and 90;        # ![5, 90]
select id, username from user1 where id not in (1, 2, 3, 4, 5);

select id, username from user1 where id is not null;
select id, username from user1 where id is null;

LIKE 通配符

_:       单个字符
%:       0 个或者多个

select * from user1;
| id  | username |
+-----+----------+
|   0 | test0    |
|   1 | test1    |
|   2 | test2    |
|   3 | test3    |
|   4 | test4    |
|   5 | test5    |
|   6 | test6    |
|   7 | test7    |
|   8 | test8    |
|   9 | test9    |
| 100 | test100  |
| 111 | test111  |

---

select * from user1 where id like ‘1__‘;

| id  | username |
+-----+----------+
| 100 | test100  |
| 111 | test111  |

select * from user1 where username like ‘test___‘;

| id  | username |
+-----+----------+
| 100 | test100  |
| 111 | test111  |

select * from user1 where username like ‘test1%‘;

| id  | username |
+-----+----------+
|   1 | test1    |
| 100 | test100  |
| 111 | test111  |

order

select id, username from users order by username;
select id, username from users order by username asc, id asc;
select id, username from users order by id desc;

默认是 asc (升序), 降序 (DESC)

limiit

limit 3         (只显示 3 位数)
limit 10, 10    (返回排名 11 到 20)
limit 1, 1      (表示第二位)

用于实现分页

别名

select id as userId, username as userName from user;
select id, username from user;                        # 两个字段
select id username from user;                         # 一个字段, username 是 id 的别名
select id as username from user;                      # 一个字段, 别名

distinct

truncate table user1;

insert into user1 (id, username) values (1, ‘test‘);
insert into user1 (id, username) values (1, ‘test‘);
insert into user1 (id, username) values (1, ‘test‘);
insert into user1 (id, username) values (1, ‘test‘);

select distinct * from user1;

SQL -- select

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