DDL: changing database structure
Data Definition Language defines database objects such as tables and constraints. CREATE, ALTER and DROP belong here. Schema changes serve a different purpose from reading or changing rows.
A concrete example
Before adding a required field to an existing table, plan how to populate old rows and whether older application versions remain compatible.
ALTER TABLE orders ADD COLUMN note text;Explain it yourself
What migration steps are needed to add a NOT NULL column to a populated table?
How to study this
Write your reasoning first. Check the original documentation, identify an assumption, then try a different example. Reading this page does not count as verified skill evidence.
Source and review
Original RealDeveloper explanation; last source check: .