a、条件判断where
select * from 表 where id > 1 and name != ‘alex‘ and num = 12; select * from 表 where id between 5 and 16; select * from 表 where id in (11,22,33) select * from 表 where id not in (11,22,33) select * from 表 where id in (select nid from 表)
b、通配符like(模糊查找)
select * from 表 where name like ‘liu%‘ # liu开头的所有(多个字符串) select * from 表 where name like ‘liu_‘ #liu开头的所有(一个字符) select * from 表 where name like ‘%liu_‘ select * from 表 where name like ‘_liu_‘ select * from 表 where name like ‘%liu%‘ select * from 表 where name like ‘_liu%‘
c、限制limit(分页)
select * from 表 limit 5; - 前5行 select * from 表 limit 4,5; - 从第4行开始的5行 select * from 表 limit 5 offset 4 - 从第4行开始的5行
d、排序asc,desc
select * from 表 order by 列 asc - 根据 “列” 从小到大排列 select * from 表 order by 列 desc - 根据 “列” 从大到小排列 select * from 表 order by 列1 desc,列2 asc - 根据 “列1” 从大到小排列,如果相同则按列2从小到大排序
e、分组group by
select num from 表 group by num select num,nid from 表 group by num,nid select num,nid from 表 where nid > 10 group by num,nid order by nid desc select num,nid,count(*),sum(score),max(score),min(score) from 表 group by num,nid select num from 表 group by num having max(id) > 10 特别的:group by 必须在where之后,order by之前
f、组合union、union all
组合,自动处理重合(去掉相同) select nickname from A union select name from B 组合,不处理重合(所有的都显示) select nickname from A union all select name from B
g、连表join
无对应关系则不显示 select A.num, A.name, B.name from A,B Where A.nid = B.nid 无对应关系则不显示 select A.num, A.name, B.name from A inner join B on A.nid = B.nid A表所有显示,如果B中无对应关系,则值为null select A.num, A.name, B.name from A left join B on A.nid = B.nid B表所有显示,如果B中无对应关系,则值为null select A.num, A.name, B.name from A right join B on A.nid=B.nid
时间: 2024-10-23 22:40:00