轉： https://www.php.cn/mysql-tutorials-474077.html#:~:text=%20sql%E7%AD%9B%E9%80%89%E5%87%BA%E9%87%8D%E5%A4%8D%E6%95%B0%E6%8D%AE%E7%9A%84%E6%96%B9%E6%B3%95%EF%BC%9A%E4%BD%BF%E7%94%A8%E2%80%9Cselect%20%2A,from%20%E8%A1%A8%E5%90%8D%20where%20%E6%9D%A1%E4%BB%B6%E2%80%9D%E8%AF%AD%E5%8F%A5%E6%9D%A5%E7%AD%9B%E9%80%89%E9%87%8D%E5%A4%8D%E6%95%B0%E6%8D%AE%EF%BC%9B%E5%8F%AF%E4%BB%A5%E4%BD%BF%E7%94%A8%E4%B8%80%E4%B8%AA%E6%88%96%E8%80%85%E5%A4%9A%E4%B8%AA%E8%A1%A8%EF%BC%8C%E8%A1%A8%E4%B9%8B%E9%97%B4%E4%BD%BF%E7%94%A8%E9%80%97%E5%8F%B7%EF%BC%88%2C%EF%BC%89%E5%88%86%E5%89%B2%EF%BC%8C%E5%B9%B6%E4%BD%BF%E7%94%A8WHERE%E8%AF%AD%E5%8F%A5%E6%9D%A5%E8%AE%BE%E5%AE%9A%E6%9F%A5%E8%AF%A2%E6%9D%A1%E4%BB%B6%E3%80%82
sql篩選出重復數據的方法：使用“select * from 表名 where 條件”語句來篩選重復數據；可以使用一個或者多個表，表之間使用逗號（,）分割，並使用WHERE語句來設定查詢條件。
本教程操作環境：windows7系統、mysql8版本、Dell G3電腦。
在電腦上打開數據庫，這里新建一張含有重復數據的user表做示例。
查詢出了數據庫中user表的重復數據。
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select * from user where name in (select name from user group by name having count(name) > 1)
刪除姓名重復的數據
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delete from user where name in (select name from user group by name having count(name) > 1)
去掉重復數據，這里去掉了張三的重復數據
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select distinct name from user
去掉班級相同的重復數據
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select distinct class from user
去掉兩個字段的重復數據
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select distinct name,class from user