I think you need to try doing something like this on your MySQL if you have admin privilege on your MySQL.
ALTER TABLE tablename MODIFY columnname DECIMAL(M,D)
for the M,D variables, read this - http://dev.mysql.com/doc/refman/5.0/en/fixed-point-types.html
And MySQL should be able to automatically converting a text to a numeric. Just that the data type in MySQL might not be a decimal yet that's why you can't store any decimal.