SQL SERVER 查詢、刪除重復數據

查詢刪除重復數據，只保留一條記錄：

1.根據單字段，查詢表中該字段重復出現記錄：

SELECT * FROM Table
WHERE Parameter IN
(SELECT Parameter FROM Table
GROUP BY Parameter HAVING COUNT(Parameter ) > 1)

分析：
SELECT Parameter FROM Table
GROUP BY Parameter HAVING COUNT(Parameter ) > 1
根據字段分組，查詢出表中出現重復（字段數量>1）的字段集

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2.根據單字段，刪除表中該字段重復出現記錄，保留最小主鍵ID

DELETE FROM Table
WHERE Parameter IN
(SELECT Parameter FROM Table
GROUP BY Parameter HAVING COUNT(Parameter) > 1)
AND ID NOT IN
(SELECT MIN(ID) FROM Table
GROUP BY Parameter HAVING COUNT(Parameter)>1)

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3.根據多個字段查詢表中重復的記錄

SELECT * FROM Table a
WHERE EXISTS
(SELECT Para1 ,Para2 FROM Table b
WHERE a.Para1 = b.Para1 AND
a.Para1 = b.Para2 GROUP BY Para1 ,Para2
HAVING COUNT(*) > 1 )

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4.根據多個字段 刪除表中重復的記錄，保留最小主鍵記錄

DELETE A
FROM Table A ,
(SELECT Para1,Para2 FROM Table
GROUP BY Para1,Para2
HAVING COUNT(*) > 1 ) B
WHERE A.Para1=B.Para1 AND a.Para2= b.Para2
AND A.ID NOT IN (SELECT MIN(ID) AS ID
FROM Table
GROUP BY Para1,Para2
HAVING COUNT(*) > 1)

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5.查詢多個字段重復記錄，不包含最小主鍵ID

SELECT * FROM Table a
WHERE EXISTS
(SELECT Para1,Para2 FROM Table b
WHERE a.Para1 = b.Para1 AND a. Para2 = b.Para2
GROUP BY Para1,Para2
HAVING COUNT(*) > 1)
AND ID NOT IN
(SELECT MIN(ID) FROM Table
GROUP BY Para1,Para2
HAVING COUNT(*)>1)

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