SQL 删除表中的重复记录，只保留其中一条。

第一步：查询重复记录

SELECT * FROM TableName  --表名
WHERE RepeatFiled IN (  
    SELECT RepeatFiled  --重复字段
    FROM TableName  
    GROUP BY RepeatFiled  
    HAVING COUNT(RepeatFiled) > 1  
)  

把重复条数大于1的全部查询出来。

第二步：删除重复记录，只保留一条

SELECT * FROM TableName  
WHERE RepeatFiled IN (  
    SELECT RepeatFiled  
    FROM TableName  
    GROUP BY RepeatFiled  
    HAVING COUNT(RepeatFiled) > 1  
    AND  
    ID NOT IN (  
        SELECT MIN(ID)  
        FROM TableName  
        GROUP RepeatFiled  
        HAVING COUNT(RepeatFiled) > 1      
    )  
)  

在第一步的基础上继续过滤，把最小值留下。