SQL Functions - Math Functions
Just like how programming languages have functions built-in to allow you to do common tasks easily. So does SQL. A lot of these functions are mathematical. Some of them are more useful than others.

Using Data Manipulation Functions
In this tutorial, you'll learn what functions are, what types of functions MySQL supports, and how to use these functions.

SQL Functions - String Functions
SQL provides a large amount of functions for string manipulations. Learn how to convert and use SQL Functions.

[MYSQL] functions/queries list
A list of usefully mysql functions and queries with short description for each function and exmaples.

SQL Date Functions - Converting and Using
SQL provides a lot of functions for manipulating dates in a database. You can store values in a date field or a datetime field. If you store the dates as unix_timestamps you can get a lot more flexibility with dates. In fact, this is usually what is done when you are using PHP with the database.

5 Useful MySQL Functions And Control Flows
If statements have been a life saver on many occasions. They are invaluable for checking a value then returning another value different from the one stored in the table...

Summarizing Data
In this tutorial, you will learn what the SQL aggregate functions are and how to use them to summarize table data.

Creating Advanced Joins
In this tutorial, you'll learn all about additional join types what they are and how to use them. You'll also learn how to use table aliases and how to use aggregate functions with joined tables.

A Complete Guide for MySQL and PHP
A Complete Guide for MySQL and PHP with examples. List of all Important functions.

SQL Encryption Functions
There are two ways of securing data in a database: hashing and encryption. Hashing usually prevents you from obtaining the original string. Encryption allows you to obtain the original string (through decrypting). This is only possible if you know the encryption method, and the key that was used to encrypt it.

MySQL and SQL
This tutorial covers the following:
Introduction to relational databases and relational modeling; The MySQL command interpreter and the basic features of MySQL; Using SQL to create and modify databases, tables, and indexes. Using SQL to insert, delete, and update data; The SQL SELECT statement for querying, with examples of simple and advanced queries; Functions and operators in SQL and MySQL; Advanced features, including managing indexes and keys, tuning the MySQL DBMS, security, and the limitations of MySQL