WITH AS 子查詢部分【mysql5.7及以下不支持，mysql8.0及sqlserver支持】

WITH AS 子查詢部分【mysql5.7及以下不支持，mysql8.0及sqlserver支持】

子查詢部分的好處是部分查詢，不如有三個表連接在一條語句種出現多次

單個子查詢部分

with a as (select * from  Student a inner join Course b ON a.Id=b.StudentId  )select * from a 

解析：這樣在此語句種每次查詢a都是查詢了student和course表的聯查集合

 

多個查詢部分語法

with a as (select * from  Student),
b as (select * from Course)
select * from a inner join b on a.Id=b.StudentId

解析：這個多個查詢部分語法的寫法，原理和單個查詢部分一致