MySQL Regular Expressions - Regexp

💡 REGEXP

Powerful tools for matching patterns within text

Components of Regular Expressions

1. Literals: The simplest type of regex. Match the exact characters you specify.

   • Example: ‘abc’ matches “abc” in the text.

2. Metacharacters
   Define a character class. Match any single character inside the brackets.

   Mark	Description
   .	Match any single character except a newline.
   ^	Anchor the match at the start of a string.
   $	Anchor the match at the end of a string.
   []	Define a character class. Match any single character inside the brackets.
   |	Alternation operator. Match either the pattern before or the pattern after the ' | '.
   ()	Group patterns together.

3. Quantifiers: Specify how many instances of a character, group, or character class must be present in the input for a match to be found.

   Mark	Description
   *	Match 0 or more instances.
   +	Match 1 or more instances.
   ?	Match 0 or 1 instance.
   {n}	Match exactly n instances.
   {n,}	Match n or more instances.
   {n,m}	Match between n and m instances.

4. Character Classes

   Mark	Description
   [abc]	Match any one of a, b, or c.
   [a-z]	Match any lowercase letter from a to z.
   [^abc]	Match any character except a, b, or c.

5. Escape Sequences

   Mark	Description
   \.	Match a literal period.
   \\	Match a literal backlash.
   \d	Match any digit (equivalent to [0-9]).
   \D	Match any non-digit.
   \w	Match any word character (equivalent to [a-zA-Z0-9_]).
   \W	Match any non-word character.
   \s	Match any whitespace character (spaces, tabs, etc.).
   \S	Match any non-whitespce character.

Advanced Concepts

1. Greedy vs. Lazy Matching
   • Greedy: a.*b matches the longest possible string starting with a and ending with b.
   • Lazy: Adding ? after a quantifier makes it lazy. a.*?b matches the shortest possible string starting with a and ending with b.
2. Lookahead and Lookbehind Assertions: Specify a condition that must be met for a match to occur but do not consume characters in the string.

Assertions	Mark	Description
Positive Lookahead	(?=…)	Example: a(?=b) matches a if it is followed by b, but b is not part of the match.
Negative Lookahead	(?!…)	Example: a(?!b) matches a if it is not followed by b.
Positive Lookbehind	(?<=…)	Example: (?<=b)a matches a if it is preceded by b.
Negative Lookbehind	(?<!…)	Example: (?<!b)a matches a if it is not preceded by b.