SQL Query Order and Aliases

SQL Query Order and Aliases

Now that we've covered basic SELECT, FROM, and WHERE in SQL: Select, Where, From, we're ready to clean up how we reason about queries.

A beginner often reads SQL from top to bottom and assumes the database runs it that way. But SQL has two different orders:

• Written order: the order you type clauses in.
• Logical processing order: the order the database conceptually uses to produce the result.

This matters in interviews because many “simple” SQL bugs come from asking: Can I use this alias here? or Has this row already been filtered yet?

We'll use the same kind of Person table from the last lesson: people have an ID, Name, City, Country, Age, and Profession.