SQL from Zero › Module 1: How a database thinks
SQL's five families of commands
DDL, DML, DQL, TCL and DCL: the map for the rest of the course.
Lesson 6 of 33 · about 10 minutes
Video: Running a shopThe narrated video for this lesson is coming soon. The lesson below covers the same ideas.
The lesson
SQL has many commands, but they fall into five families. Think about running our bookshop's database the way you'd run a real shop.
| Family | Shop analogy | Main commands | Example |
|---|---|---|---|
| DDL, Data Definition Language | Build the shelves | CREATE, ALTER, DROP | Create a books table |
| DML, Data Manipulation Language | Stock the shelves | INSERT, UPDATE, DELETE | Add a new book, change a price |
| DQL, Data Query Language | Ask questions | SELECT | Which books cost under $10? |
| TCL, Transaction Control Language | Make each sale all-or-nothing | BEGIN, COMMIT, ROLLBACK | Undo a half-finished price update |
| DCL, Data Control Language | Hand out keys | GRANT, REVOKE | Let an intern read orders, but not delete them |
Some people count SELECT as part of DML. Either way, it's the command you'll use most.
This is also the map of this course. Next, you'll start building: writing your first CREATE TABLE and putting up the bookshop's shelves.
Key ideas
- DDL builds the structure: CREATE, ALTER, DROP.
- DML changes the data: INSERT, UPDATE, DELETE. DQL asks questions with SELECT.
- TCL makes changes all-or-nothing: BEGIN, COMMIT, ROLLBACK. DCL controls who can do what: GRANT, REVOKE.
Practise
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