Now that you know how to create a table, a proper SQL table, let’s see how you can change it without having to re-create it! Yes, it’s possible. Keep reading to find out more.
By Rafael Victória-Pereira
In the previous TechTips, I’ve created the inventory, item, and warehouse master tables. However, the relationship between these tables is not yet enforced at database level. I know, you’re used to doing this using an RPG program. However, just as in the case of the timestamp that is automatically updated by the database engine, there’s also a way to define, at table level, that the value of a certain column must be cross-checked with another table’s column. In other words, I can only use item IDs in the inventory master table that have been previously defined in the item master table. This is what’s called a foreign key. You probably have a lot of these situations in your applications—and you’re probably handling the cross-checking using RPG. Well, SQL can take care of that for you, with its equivalent to the CHGPF CL command: ALTER TABLE. You can use this SQL instruction to add or remove (drop, in SQL lingo) columns, constraints, and primary keys, among other things.
