Truncating output to a given character legnth

I am trying to transform an existing dataset to meet the specifications of a different data structure so that it can be moved. Some field lengths are off, and as such I would like to automatically cut off the existing text at that length to allow for the transfer as changing each individual record is just not practical. Is there an easy way to do this with mysql?

LEFT(foo,123) will truncate the foo column value to 123 bytes