Kyl*_*yle 8 sql join self-join
我正在尝试根据混合列找到重复的行.这是我的一个例子:
CREATE TABLE Test
(
id INT PRIMARY KEY,
test1 varchar(124),
test2 varchar(124)
)
INSERT INTO TEST ( id, test1, test2 ) VALUES ( 1, 'A', 'B' )
INSERT INTO TEST ( id, test1, test2 ) VALUES ( 2, 'B', 'C' )
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现在,如果我运行此查询:
SELECT [LEFT].[ID]
FROM [TEST] AS [LEFT]
INNER JOIN [TEST] AS [RIGHT]
ON [LEFT].[ID] != [RIGHT].[ID]
WHERE [LEFT].[TEST1] = [RIGHT].[TEST2]
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我希望能找回两个id.(1和2),但我只回到了一排.
我的想法是它应该比较每一行,但我想这不正确?为了解决这个问题,我将查询更改为:
SELECT [LEFT].[ID]
FROM [TEST] AS [LEFT]
INNER JOIN [TEST] AS [RIGHT]
ON [LEFT].[ID] != [RIGHT].[ID]
WHERE [LEFT].[TEST1] = [RIGHT].[TEST2]
OR [LEFT].[TEST2] = [RIGHT].[TEST1]
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这给了我两行,但性能根据行数极快地降低.
我为性能和结果找到的最终解决方案是使用联合:
SELECT [LEFT].[ID]
FROM [TEST] AS [LEFT]
INNER JOIN [TEST] AS [RIGHT]
ON [LEFT].[ID] != [RIGHT].[ID]
WHERE [LEFT].[TEST1] = [RIGHT].[TEST2]
UNION
SELECT [LEFT].[ID]
FROM [TEST] AS [LEFT]
INNER JOIN [TEST] AS [RIGHT]
ON [LEFT].[ID] != [RIGHT].[ID]
WHERE [LEFT].[TEST2] = [RIGHT].[TEST1]
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但总的来说,我显然不理解为什么这不起作用,这意味着我可能做错了什么.有人能指出我正确的方向吗?
Aar*_*ght 11
不要加入不平等; 似乎JOIN和WHERE条件被反转.
SELECT t1.id
FROM Test t1
INNER JOIN Test t2
ON ((t1.test1 = t2.test2) OR (t1.test2 = t2.test1))
WHERE t1.id <> t2.id
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应该工作正常.
如果您选择它们,您只能取回两个ID:
SELECT [LEFT].[ID], [RIGHT].[ID]
FROM [TEST] AS [LEFT]
INNER JOIN [TEST] AS [RIGHT]
ON [LEFT].[ID] != [RIGHT].[ID]
WHERE [LEFT].[TEST1] = [RIGHT].[TEST2]
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只获得一个ROW的原因是只有一行(即第2行)的TEST1等于另一行的TEST2.