Update on 5/20/2019: it is no longer a free book, now available on Amazon, here. 

This book is a guide to using SQL to retrieve data from databases. This site includes a 'Practice SQL' environment where you can try out the examples from the book and experiment with SQL queries. This book is available here. 

Contents

1. Prerequisites..............4

2. Instructions................4

3. Joining tables.............6

4. SQL ...........................8

5. Single-table operations ..........9

• Selecting columns..9
• Selecting rows......12

6. Sorting result tables.14

7. Counting rows.........15

8. Summing totals........16

9. Cartesian Joins.........20

10. Retrieving data from multiple tables...........21

11. Distinct values.........25

12. Union.......................27

13. Subqueries...............28

• Updating data ..........29
• Inserting records ...........29
• Updating records ..........29
• Deleting records ...........30

15. NULL values...........31

16. About the Author.....32

17. Appendix A – Implementation variations..........33

18. Appendix B – Summary of operators...........34

19. Appendix C – Other statements ...........35

20. Appendix D – Test environment ...............36