validation within a database

basically i need to know how to do simple validation checking on fields for my database (i.e if declared as Integer, they type string then will interrupt error). I'm sure this is a simple problem to deal with but i don;t know how to do it. THanks for any help you can give me
CHEERS

If you are using a DBMS (like access/SQL server) just set the appropriate data type for each column. The database engine will raise an error if the wrong type of data is entered into that field