If you use the FIND_IN_SET
function:
FIND_IN_SET(a, columnname)
yields all the records that have "a" in them, alone or with others
AND
FIND_IN_SET(columnname, a)
yields only the records that have "a" in them alone, NOT the ones with the others
So if record1 is (a,b,c) and record2 is (a)
FIND_IN_SET(columnname, a)
yields only record2 whereas FIND_IN_SET(a, columnname)
yields both records.