So last week I got an email from our host saying a database has received its maximum size of 3GB. I was like what? How? So I quickly ran the below to check which column was causing the problem.
If you want to find out the size of column=COLUMN_NAME from table=TABLE_NAME, you can always run a query like this:
SELECT sum(char_length(COLUMN_NAME))FROM TABLE_NAME;
Size returned is in bytes. If you want it in kb, you could just divide it by 1024, like so:
SELECT sum(char_length(COLUMN_NAME))/1024FROM TABLE_NAME;