SQL分組查詢問題;根據一個字段的值對一組行進行評估

Question

我有表供應商部件列出了我所有的零件及其供應商。具有多個供應商的零件在此表中有多個記錄。我試圖編寫一個只返回partid的查詢，以及沒有分配默認供應商的零件的供應商。

Partid  Vendor  Defaultflag 
1   A   1 
2   B   0 
2   C   0 
3   D   0 
3   E   0 
3   F   1 
4   G   0 

我想返回如下：

Partid  Vendor 
2   B 
2   C 
4   G 

我顯然具有PARTID 3個問題，並獲取查詢看到它具有指定默認的供應商。

Answer 1

使用內部選擇查找沒有默認供應商的部件。這是partid分組時MAX(Defaultflag) = 0的部分。然後您可以將其加入到原始表中以獲取所有行。下面是完整的查詢：

SELECT T2.Partid, T2.Vendor 
FROM (
    SELECT Partid 
    FROM Table1 
    GROUP BY Partid 
    HAVING MAX(Defaultflag) = 0 
) T1 
JOIN Table1 T2 
ON T1.PartId = T2.PartId 

結果：

2, 'B' 
2, 'C' 
4, 'G' 

Answer 2

和空 - 左 - 加入方法：

SELECT vp0.Partid, vp0.Vendor 
FROM VendorParts AS vp0 
LEFT JOIN VendorParts AS vp1 ON vp1.Partid=vp0.Partid AND vp1.Defaultflag=1 
WHERE vp1.Partid IS NULL 

Answer 3

你可以嘗試像

DECLARE @VendorParts TABLE(
     Partid INT, 
     Vendor VARCHAR(10), 
     Defaultflag INT 
) 
INSERT INTO @VendorParts SELECT 1,'A',1 
INSERT INTO @VendorParts SELECT 2,'B',0 
INSERT INTO @VendorParts SELECT 2,'C',0 
INSERT INTO @VendorParts SELECT 3,'D',0 
INSERT INTO @VendorParts SELECT 3,'E',0 
INSERT INTO @VendorParts SELECT 3,'F',1 
INSERT INTO @VendorParts SELECT 4,'G',0 

SELECT * 
FROM @VendorParts vp 
WHERE NOT EXISTS (
         SELECT 1 
         FROM @VendorParts 
         WHERE Partid = vp.Partid 
         AND  Defaultflag = 1 
        ) 

輸出

Partid  Vendor  Defaultflag 
----------- ---------- ----------- 
2   B   0 
2   C   0 
4   G   0 

Answer 4

像

select 
partid, 
vendor 
from 
vendorparts 
where 
partid not in (
    select 
    partid 
    from 
    vendorparts 
    where 
    defaultflag = 1 
);