mysql 多表查询 比较两个字段最大、最小值，并显示对应字段

: select max(date) from ( select max(date) date from A unoin all select max(date) date from B ) a

最大值：select max(num) from table

第二大值：select max(num) from table

where num not in(select max(num) from table)

第三大值：select max(num) from table

where num not in(select max(num) from table

where num not in(select max(num) from table))

最小值：select min(num) from table

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