数据库查询条件常用 数据库单表查询总结

select disintct col1,col2,col3 from tab_name order by col2,col3;##ORACLE上的语法.一定要按其他两个字段排序只能这么写.

select * from blh where blh='1066' or blh ='2100' 或select * from blh where blh in ('1066' ,'2100')

select * from tb_user where substring(username, 2,1)='阳' 呃` 是这个,上面搞错了,嘎嘎

IFNULL 函数即可 SELECT * FROM db_staff AS user WHERE user.id = IFNULL(id, user.id) AND user.`name` = IFNULL(name, user.`name` ) AND user.role = IFNULL(role, user.role) 也就是 如果参数 id 是 null,那么 user.id = IFNULL(id, user.id) 就相当于 user.id = user.id

select t1.* from table1 t1,table1 t2where t1.姓名=t2.姓名 and ((t1.数据=1 and t2.数据=2) or (t1.数据=2 and t2.数据=1))

select vs_id,vu_user_id,count(vs_id) 出现次数 from 表 group by vu_user_id,vs_id查询结果:vs_id vu_user_id 出现次数1 1 11 2 12 2 13 2 23 11 24 2 15 2 1

假设所有 字段 都在一张 学生表 里 select * from 学生表 where 课程号=4 and 成绩 > 80

select student.[学号(sno)], student.[姓名(sname)] from student, sc where student.[学号(sno)]=sc.sno and sco='4' and sc.grade>80;

sql中可以有多个where 条件.可以反复的嵌套.例如:select * from 表1where 字段1 in (select 字段2 from 表2 where 查询条件)and 字段3 in (select 字段4 from 表3 where 查询条件 )

是用模糊查询 select * from student where name like ＂(a~k)%＂