1. Arrays (6632/-)
2. Assignment statements (4309/-)
3. Associative Arrays (4760/-)
4. Case-Sensitivity (5356/-)
5. Comments (6143/-)
6. Common string constants (4427/-)
7. Create thumbnails using PHP (12110/-)
8. Dates (5978/-)
9. End of statement (4197/-)
10. Equality (3420/-)
11. For loops (4157/-)
12. Get a user's IP address (10376/-)
13. HTML encoding functions (6700/-)
14. If statements (5279/-)
15. Loosely Typed Variables (3807/-)
16. MySQL - 'INSERT..SELECT' copies data from a SELECT into a table (12185/-)
17. MySQL - Adding or Subtracting days (8431/-)
18. MySQL - Components of a date (5726/-)
19. MySQL - Concatenate strings (48771/-)
20. MySQL - Conditional values (17562/-)
21. MySQL - CREATE a new table (6469/-)
22. MySQL - Delete (12147/-)
23. MySQL - DROP an unwanted table (5111/-)
24. MySQL - Explicitly enter a NULL (4412/-)
25. MySQL - Find the Insert ID (6288/-)
26. MySQL - Finding a substring in a string (15951/-)
27. MySQL - Finding out your tables (4315/-)
28. MySQL - Format dates (10892/-)
29. MySQL - Formatting numbers to two decimal places (16604/-)
30. MySQL - Get the 11th to the 20th rows of the Squeek table - by UserName (4969/-)
31. MySQL - Get the date and time right now (9101/-)
32. MySQL - Get the first 10 rows of the Squeek table (5021/-)
33. MySQL - Insert (14214/-)
34. MySQL - Insert a date (22923/-)
35. MySQL - Joining two tables (11767/-)
36. MySQL - Match a range of dates (9204/-)
37. MySQL - Match a specific date (4920/-)
38. MySQL - Replace a NULL with a specific value (12884/-)
39. MySQL - Select - including strtolower() (12634/-)
40. MySQL - Select random row (27558/-)
41. MySQL - SELECT within SELECT (28964/-)
42. MySQL - Substring: Extracting part of a string (23531/-)
43. MySQL - Update (12006/-)
44. MySQL - uppercase / lowercase (14970/-)
45. MySQL - What are the columns of the Squeek table? (3991/-)
46. Need to declare variables? (5231/-)
47. PHP - Random Number (16289/-)
48. PHP - Sending Email (9920/-)
49. Print 1 to 10 on a web page (4892/-)
50. Regular Expressions (4803/-)
51. Script Tags (4798/-)
52. Sending HTML to Browser (3815/-)
53. String Concatenation (9688/-)
54. String Evaluation (4867/-)
55. Strings (3799/-)
56. Switch/Case (4243/-)
57. True and False (3515/-)
58. Variables (3314/-)
59. While statements (3771/-)

Example 1
SELECT name FROM cia WHERE population > (SELECT population FROM cia WHERE name='United States')

Example 2
SELECT name FROM cia WHERE region = (SELECT region FROM cia WHERE name = 'Brazil')