如何选择表中包含最长字符串信息的文本列

Question

I am selecting columns like this:

    SELECT table_name, column_name
    FROM information_schema.`COLUMNS` 
    WHERE table_schema ='db_name' 
      AND data_type IN ('varchar', 'text') 
      AND table_name='table_name';

The result is a table name and column name on each row. In the third column I would like to see a number of bytes of the longest string in that column of the table.

I am trying to optimize a table becouse when I am trying to convert data from latin2 to utf8 I get the "Row size too large." error. So I want to change varchar (255) to lower number if possible. I would like to avoid changing columns to TEXT if it will be possible.

Answer 1

The mysql function you are looking for is the length() function http://dev.mysql.com/doc/refman/5.1/en/string-functions.html#function_length

Combined with max(length(COLUMN_NAME)) and a group by statement, you should be fine.