Introduction to SQL

SQL (originally SEQUEL, from IBM) stands for Structured Query Language. It is the standard language for interacting with relational databases.

  • It is not the only way to do so, but it is by far the most popular.
  • There are slight variations from platform to platform ("dialects of SQL").

Interactive Learning

This eBook is designed to be fully interactive. The SQL code blocks you see throughout the chapters run entirely within your web browser using SQLite (compiled via WebAssembly). This means there is no round trip to a remote database server—your queries execute locally and instantly on your machine.

How to use SQL code blocks:

  1. View: Read the query provided in the editor.
  2. Edit: You can click directly inside the code block to modify the statements or write your own queries. Your edits are saved in your browser. You can reset them at any time.
  3. Run: Click on the Run Query button to execute the query against the active database.
  4. Observe: The results (records and columns) will appear immediately in the Output table.
SQL Editor Tips & Context
  • Persistent Context: All SQL blocks on the same page share a single active in-memory database instance. If you create a table or insert records in one block and run it, those changes will be available in any subsequent SQL blocks you execute on that page! Remember that execution order is what matters, not the visual top-to-bottom layout of cells.
  • Refreshing the Page: Refreshing your browser will reset the in-memory database and clear any tables or records you created. However, any code modifications you wrote in the boxes are preserved.
  • Reset Code Button: If you want to undo your edits and restore a code block to its original state, click Reset Code.
  • Context Suffixes:
    • sql (Shared): Database state and tables are shared across all standard blocks on the same page. The system dynamically isolates database environments by page name so they do not pollute other chapters.
    • sql-isolated (Isolated): Creates a private, independent database sandbox for that specific block.

Good tutorials/textbooks: