MySQL has many built-in functions that can be used to manipulate
data contained within columns. With these functions, you can format data,
extract text, or create search expressions. In and of themselves,
functions do not affect data within columns. Instead, they manipulate data
within results of queries. However, when used properly within SQL
statements such as UPDATE, they can be a tool for changing
data within columns. Incidentally, functions can be used for processing
plain text or numbers—they don’t require that data come from a
column.
There are three major groupings of functions: string functions; date and time functions; and numeric or arithmetic functions. String functions are functions that relate to formatting and converting text, as well as finding and extracting text from columns. These are covered in Chapter 10.
Date and time functions are covered in Chapter 11. These functions can be used for formatting date and time values, as well as extracting specific values from a given date or time. They can also be used to get date and time values from the system to use for inserting or updating data in columns of a table.
The numeric or arithmetic functions are used for mathematical or statistical calculations on data. They are covered in Chapter 12.
These three chapters will include the most popular and more useful functions from these three major groups of functions, but not all functions from these categories. As part of learning and developing MySQL and MariaDB, you should be aware of these functions, and learn them well.