sql语句中的having count是什么意思

select id, count() from table a where 1=1 group by id having count()>2

select id, count() from table a where 1=1 group by id having count()>2
以id分组统计，查询分组后数量大于2的id和数量

SELECT
    age 
FROM
    user
GROUP BY
    age 
HAVING
    count( age ) >= 3

查询user表中，年龄重复次数大于等于3的age，并输出age的值

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