12.6. SIMILAR TO Predicates
As you can see, the LIKE predicate is pretty weak, especially if you have used a version of grep(), a utility program from the UNIX operating system. The name is short for “general regular expression parser,” and before you ask, a regular expression is a class of formal languages. If you are a computer science major, you have seen them; otherwise, don’t worry about it. The bad news is that there are several versions of grep() in the UNIX community, such as egrep(), fgrep(), xgrep(), and a dozen or so others.
The SQL-99 standard added a regular expression predicate of the form <string expression> SIMILAR TO <pattern>, which is based on the POSIX version of grep() found in ISO/IEC 9945.
The special symbols in a pattern ...
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