检查表列已达最大长度

Question

只是想知道是否有办法检查达到最大长度的表的列。

有了下面我能得到表列

SELECT MAX(CHARACTER_MAXIMUM_LENGTH) AS LEN, COLUMN_NAME 
FROM information_schema.columns 
WHERE table_name IN ('TableA') 
GROUP BY COLUMN_NAME 
ORDER BY LEN DESC 

然后我想检查的长度那些列是否达到其最大长度或不符合数据

列出了最大长度列

SELECT MAX(LENGTH(Col1)) 
FROM TableA 

由于它是不可能在WHERE子句中使用聚合函数，它是如何可能？

感谢

Answer 1

您可以使用join带来的数据一起：

SELECT MaxLen, ActualLen 
FROM (SELECT MAX(CHARACTER_MAXIMUM_LENGTH) AS MaxLen, COLUMN_NAME 
     FROM information_schema.columns 
     WHERE table_name IN ('TableA') AND COLUMN_NAME = 'COL1' 
    ) m CROSS JOIN 
    (SELECT MAX(LENGTH(Col1)) as ActualLen 
     FROM TableA 
    ) c; 

我不知道你真正想要返回什么。如果您想要最大值的行：

select a.* 
from tablea a 
where length(col1) = (SELECT MAX(CHARACTER_MAXIMUM_LENGTH) AS MaxLen 
         FROM information_schema.columns 
         WHERE table_name IN ('TableA') AND COLUMN_NAME = 'COL1' 
        );