MySQL Sub-query

1. Where sub-query

(The inner query result is treated as the comparison condition of the outer query )

#不用order by to find the latest products

Select  from where = (selectmax from goods);

#取出每个栏目下最新的产品 (goods_id only)

Select  from where inch (selectmaxfromgroup by

2, from type sub-query

(The inner query results for the outer layer again query )
#用子查询查出挂科两门及以上的同学的平均成绩
Ideas:
#先查出哪些同学挂科两门以上

Select name,count(*as fromwhere<  having >= 2;

#以上查询结果, we just have to name it, so we take a name again.

Select  from (Select name,count(*as from have>=2  as T;

#找出这些同学了, then calculate their average score.

Select name,avgfrom thewhere in (select name,count(*as from having>=2  as Group  by name;

3, Exists type sub-query

(Take the outer query results to the inner layer , see if the inner layer of the query is established)
#查询哪些栏目下有商品, column list category, Commodity table goods

Select  from where exists (Select*fromwhere= category.cat_id);

MySQL Sub-query