查询删除重复数据，只保留一条记录：
1.根据单字段，查询表中该字段重复出现记录：
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
根据字段分组，查询出表中出现重复（字段数量>1）的字段集
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2.根据单字段，删除表中该字段重复出现记录，保留最小主键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.根据多个字段查询表中重复的记录
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.根据多个字段 删除表中重复的记录，保留最小主键记录
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.查询多个字段重复记录，不包含最小主键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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