在MySQL单个表中找到重复的值

1、一个表中单个列重复的值

SELECT
    id,
    firstName,
    lastName,
    email,
    COUNT(*)
FROM
    contacts
GROUP BY
    firstName
HAVING
    COUNT(firstName) > 1;

结果是：其中count(*)是表示重复的次数。

 2、在多个列中查找重复值

SELECT
    id,
    firstName,
    lastName,
    email,
    COUNT(*)
FROM
    contacts
GROUP BY
    firstName,
    lastName,
    email
HAVING
    COUNT(firstName) > 1
AND COUNT(lastName) > 1
AND COUNT(email) > 1;

结果：

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