什麼更好，WITH語句或左連接3個表？

Question

Plz告訴我在mssql中的2個查詢之間有什麼更好？

;with ab as (select a.*,b.CategoryName from Products a 
left join Categories b on a.CategoryID = b.CategoryID where b.CategoryID = 2) 
select * from ab left join Suppliers c on ab.SupplierID = c.SupplierID 

或

select * from Products a left join Categories b on a.CategoryID = b.CategoryID 
left join Suppliers c on a.SupplierID = c.SupplierID 
where b.CategoryID = 2 

Answer 1

是相同的，只有WITH幫助，使代碼更易讀。

您可以測試它與EXPLAIN QUERY How do I obtain a Query Execution Plan?