[Documentation:InstructorUI] Expand SQL Doc.

[expliKate]

Expanded SQL documentation, basing terminology and level of detail on the assumption of an audience that is nearly or mostly new to SQL. This is in response to issue #7604, which suggests adding example code and simple instructions for novice SQL users to the existing documentation.

At a minimum, this should be reviewed for:

• language conforming to existing documentation
• level of detail appropriate for novices and beginners
• whether formatting and organization convey ideas as clearly as possible

[expliKate]

This documentation section could probably be expanded even further, so I'm unsure whether this should close issue #7604 if these changes are accepted.