10.20 MYSQL查找总结

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

10.20 MYSQL查找总结

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