SQL Server不同，選擇所有行

Question

我在這個主題上看到了很多問題和答案，但我很難理解我在做什麼錯誤，下面的查詢獲取我需要的所有信息，但是如果它有多行，當r_num是相同的，並且每個r_num的r_order是相同的，那麼對於每個r_num我只有一個結果，現在雖然這個調用給了我錯誤，有人請向我解釋Distinct是如何工作的，我該如何使用它在此查詢實現我的目標是什麼？

SELECT DISTINCT po_num, r_num, r_order, vendor, order_date, received_by, received_date FROM(
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date 
    FROM Parts.dbo.po as p INNER JOIN 
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN 
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar) 
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date) as tbl 
GROUP BY r_num, r_order 

以下是錯誤我得到

Msg 8120, Level 16, State 1, Line 1 Column 'tbl.po_num' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Answer 1

除非你在做聚合，否則你不需要同時擁有DISTINCT和GROUP BY。

SELECT DISTINCT po_num, r_num, r_order, vendor, order_date, received_by, received_date 
FROM 
    (
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date 
    FROM Parts.dbo.po as p INNER JOIN 
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN 
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar) 
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date 
) as tbl 

如果你想獲得不同r_num和r_order值，則需要任何一組由/只選擇兩列：

SELECT r_num, r_order 
FROM 
    (
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date 
    FROM Parts.dbo.po as p INNER JOIN 
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN 
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar) 
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date 
) as tbl 
GROUP BY r_num, r_order 

或者，如果你的數據可以處理它，使用額外列上的聚合：

SELECT MAX(po_num) AS po_num, r_num, r_order, MAX(vendor) AS vendor -- etc. 
FROM 
    (
    SELECT p.id as po_num, r.id as r_num, r.rec_order as r_order, v.name as vendor, p.order_date, r.received_by, r.received_date 
    FROM Parts.dbo.po as p INNER JOIN 
    Parts.dbo.vendor as v ON v.id = p.vendor__id INNER JOIN 
    Parts.dbo.receipts as r ON r.id = 'R-'+CAST(p.id AS varchar) 
    GROUP BY p.id, r.id, r.rec_order, v.name, p.order_date, r.received_by, r.received_date 
) as tbl 
GROUP BY r_num, r_order