Database Reference
In-Depth Information
9
Expressions
In this chapter, you learn how to use regular expressions within MariaDB
WHERE
clauses for greater control over data filtering.
The filtering examples in the previous two chapters enabled you to locate data
using matches, comparisons, and wildcard operators. For basic filtering (and
even some not-so-basic filtering) this might be enough. But as the complex-
ity of filtering conditions grows, so does the complexity of the
WHERE
clauses
themselves.
And this is where regular expressions become useful. Regular expressions are
part of a special language used to match text. If you needed to extract phone
numbers from a text file, you might use a regular expression. If you needed to
locate all files with digits in the middle of their names, you might use a regular
expression. If you wanted to find all repeated words in a block of text, you
might use a regular expression. And if you wanted to replace all URLs in a
page with actual HTML links to those same URLs, yes, you might use a regu-
lar expression (or two, for this last example).
Regular expressions are supported in all sorts of programming languages, text
editors, operating systems, and more. And savvy programmers and network
managers have long regarded regular expressions as a vital component of their
technical toolboxes.
Regular expressions are created using the regular expression language, a spe-
cialized language designed to do everything that was just discussed and much
more. Like any language, regular expressions have a special syntax and instruc-
tions that you must learn.
