目录
where
比较运算符查询
- 等于: =
- 大于: >
- 大于等于: >=
- 小于: <
- 小于等于: <=
- 不等于: != 或 <>
例1:查询编号大于3的学生:
select * from students where id > 3;
例2:查询编号不大于4的学生:
select * from students where id <= 4;
例3:查询姓名不是“黄蓉”的学生:
select * from students where name != '黄蓉';
例4:查询没被删除的学生:
select * from students where is_delete=0;
逻辑运算符查询
- and
- or
- not
例1:查询编号大于3的女同学:
select * from students where id > 3 and gender=0;
例2:查询编号小于4或没被删除的学生:
select * from students where id < 4 or is_delete=0;
例3:查询年龄不在10岁到15岁之间的学生:
select * from students where not (age >= 10 and age <= 15);
模糊查询
- like是模糊查询关键字
- %表示任意多个任意字符
- _表示一个任意字符
例1:查询姓黄的学生:
select * from students where name like '黄%';
例2:查询姓黄并且“名”是一个字的学生:
select * from students where name like '黄_';
例3:查询姓黄或叫靖的学生:
select * from students where name like '黄%' or name like '%靖';
范围查询
- between .. and .. 表示在一个连续的范围内查询
- in 表示在一个非连续的范围内查询
例1:查询编号为3至8的学生:
select * from students where id between 3 and 8;
例2:查询编号不是3至8的男生:
select * from students where (not id between 3 and 8) and gender='男';
SELECT * FROM students WHERE name LIKE '%三%' AND name IN ('张三', '李四', '赵六六')
空判断查询
- 判断为空使用: is null
- 判断非空使用: is not null
select * from students where height is null;
排序
select * from 表名 order by 列1 asc|desc [,列2 asc|desc,...]
- asc从小到大排列,即升序
- desc从大到小排序,即降序
- 默认按照列值从小到大排列(即asc关键字)
例1:查询未删除男生信息,按学号降序:
select * from students where gender=1 and is_delete=0 order by id desc;
例2:显示所有的学生信息,先按照年龄从大-->小排序,当年龄相同时 按照身高从高-->矮排序:
select * from students order by age desc,height desc;
分页
- limit是分页查询关键字
- start表示开始行索引,默认是0
- count表示查询条数
select * from 表名 limit start,count
select * from students where gender=1 limit 0,3;
简写
select * from students where gender=1 limit 3;
已知每页显示m条数据,求第n页显示的数据
提示: 关键是求每页的开始行索引
查询学生表,获取第n页数据的SQL语句:
select * from students limit (n-1)*m,m