一、条件查询
利用where语句可以对数据进行筛选
select * from 表名 where 条件;
二、比较运算符
运算符 | 描述 | 例子 |
= | 等于 | where id = 1 |
\> | 大于 | where age > 10 |
< | 小于 | where age < 10 |
>= | 大于等于 | where age >= 10 |
<= | 小于等于 | where age <= 10 |
!= | 不等于 | where name != '老王' |
select * from users where id = 1;
三、逻辑运算符
运算符 | 描述 | 例子 |
and | 并且 | where id = 1 and age > 10 |
or | 或者 | where id = 1 or age > 10 |
not | 取反 | where not id = 1 |
select * from users where id = 1 and age = 24;
select * from users where not id = 1;
四、范围查询
运算符 | 描述 | 例子 |
in | 在指定的非连续范围内 | where id in(1,3,5); |
between ... and ... | 在指定的连续范围内 | where id between 1 and 5; |
select * from users where id in (1,3,4);
select * from users where id between 1 and 5;
五、空判断
运算符 | 描述 | 例子 |
is null | 判断是否为空 | where name is null |
is not null | 判断是否不为空 | where name is not null |
注：null与''是不一样的
INSERT INTO users (name, birth_date, phone,age)
VALUES ('', '1990-01-01', '13813145213',30);
INSERT INTO users (name, birth_date, phone,age)
VALUES (null, '1990-01-01', '13813145213',30);
INSERT INTO users (name, birth_date, phone,age)
VALUES ('老张', null, '17813145213',30);
select * from users where birth_date is null;
六、模糊查询
运算符 | 描述 | 例子 |
like | 简单的模式匹配 | where name like '老王' |
where name like '老王%' | 以老王开头 | |
where name like '%老王' | 以老王结尾 | |
where name like '%老王%' | 任意地方包含老王 | |
where name not like '%老王%' | 任意地方都不包含老王 |
select * from users where name like '王%';
select * from users where name like '%王';
七、优先级
- 小括号，not，比较运算符，逻辑运算符
- and比or先运算，如果同时出现并希望先算or，需要结合()使用
