A string is a value that can contain alphabetical characters, digits, and other characters (e.g., the ampersand, the dollar sign). Although a string can contain numbers, they are not considered numeric values. It’s a matter of context and perspective. For instance, postal codes in the United States are all digits, but you shouldn’t store them as integers because the postal code for 02138 would become 2138. You should use a string to store the postal code.
To make the handling of strings easier, MySQL provides many built-in
functions. You can format text for nicer results, make better expressions in
WHERE clause, or otherwise extract and manipulate data from a
string or column. Therefore, in this chapter, we’ll go through several
string functions, grouping them by similar features, and provide examples of
how they might be used.