SELECT and JOIN

https://www.mysqltutorial.org/mysql-inner-join.aspx

Time/date

http://www.richardlord.net/blog/dates-in-php-and-mysql

http://www.tizag.com/perlT/perlmysqlquery.php

http://bytes.com/serversidescripting/perl/tutorials/perlandmysql-together/index.html

http://weblogs.sqlteam.com/jeffs/archive/2007/01/02/56079.aspx

http://www.bennadel.com/blog/172-Ask-Ben-Selecting-Parts-of-a-Date-Time-Stamp-In-SQL.htm

Performance

Max connections

Checking for errors in all tables/databases

• In phpMyAdmin, select database and then check the table you want to investigate. In the dropdown box "With Selected", choose the Check / Repair option, etc.

Alternately:

mysqlcheck -c -u root -p --all-databases

Repair a database

mysqlcheck -r DATABASE_NAME -u root -p