常用SQL语句加案例

原图

//进行乘法运算

select *,age*2 from user_student;

字符串做算术运算时，会被当做0来进行运算，在字符串中+号不代表拼接

//通过where条件查询user_student表下age大于22的数据

select id,name,age from user_student where age > 22;

//通过where条件查询 between 关键字设置范围查询年龄在20到30之间的数据

select id,name,age from user_student where age between 20 and 30;

// in 关键字 数据name是王五的数据

select id,name,age from user_student where name in('王五');

//模糊查询 下划线“_”可以匹配1个字符，如果要匹配0-n个字符，需要用“%”;

select * from user_student where name like '李_';

select * from user_student where name like '%四';

//按age排序，asc升序，desc降序，其中asc是可以省略的

select * from user_student order by age asc ;

select * from user_student order by age desc;

//分组查询 name出现几次 count（*） 计数

select name, count(*)from user_student group by name;

//count(*) = 2

select name, count(*)from user_student group by name having count(*) = 2;

//分页查询 limit 1,2第二行开始 查询两行

select * from user_student limit 1,2;