This came up during the rebuild of a very old legacy application. The previous app used
varchar(255) for most columns, but this seemed a bit wasteful.
To get a better idea of how large things needed to be in the new design, I wanted to know the the longest value stored for each column.
Thankfully MySQL has the
length function that can be used for this. The following query qill return a single result containing the longest value, as well as its length:
SELECT <column>, LENGTH(<column>) as col_length FROM <table> ORDER BY col_length DESC LIMIT 1
<table> with the column and table name to query.