Like ancient Gaul, SQL is divided into three sub- languages. The DDL (Data Declaration Language) declares the data. This is where we find the data types, constraints, references and other structures that have to do with how the data stored . The DML (Data Manipulation Language) uses those declarations to change their contents or to invoke them. It does not change structures and schema objects.
I’ve been telling people for years that the DDL is the most important sub- language in SQL because it defines the universe. My main gripe with the way people write DDL is that they forget