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mysql之基础二where order by limit

Star英 2022-01-08 阅读 34

目录

where

比较运算符查询

 排序

 分页


where

比较运算符查询

  1. 等于: =
  2. 大于: >
  3. 大于等于: >=
  4. 小于: <
  5. 小于等于: <=
  6. 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 

  1. and
  2. or
  3. 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

  1. like是模糊查询关键字
  2. %表示任意多个任意字符
  3. _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

  1. between .. and .. 表示在一个连续的范围内查询
  2. 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

  1. 判断为空使用: is null
  2. 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,...]
  1. asc从小到大排列,即升序
  2. desc从大到小排序,即降序
  3. 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

  1. limit是分页查询关键字
  2. start表示开始行索引,默认是0
  3. 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

 

 

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