PostgreSQL Regular Expression Query

Reference http://www.php100.com/manual/PostgreSQL8/functions-matching.html

like

 
 
string LIKE pattern [ ESCAPE escape-character ]
string NOT LIKE pattern [ ESCAPE escape-character ]

Eachpatterndefines a collection of strings. If thestringis contained in a string collection represented bypattern, thelike expression returns True. (as we imagined, if like returnstrue, then the not-like expression returns false, and vice versa.) An equivalent expression is not(stringlikepattern).)

Ifpatterndoes not contain a percent sign or an underscore, then the pattern represents itself only,and the like behaves as an equals operator. The underscore (_) in thepatternrepresents (matches) any single character, and a percent symbol (%) matches any string of zero or more characters long.

Here are some examples:

‘abc‘ LIKE ‘abc‘    true
‘abc‘ LIKE ‘a%‘     true
‘abc‘ LIKE ‘_b_‘    true
‘abc‘ LIKE ‘c‘      false

like pattern matching always overwrites the entire string. To match a sequence anywhere inside a string, the pattern must begin and end with a percent sign. The like operator can also match the specified string, but unlike the ~, a similar string is not found if it appears in the middle of the text  it, the corresponding row is not returned. and ~ in the text to match, if the matched string appears in the text, ~ will find it, the corresponding row is returned.

Table Regular expression matching operator (Note: ~ equals like)

operator	Description	Example
~	Match regular expressions, case-related	' Thomas ' ~ '. *thomas.* '
~*	Match regular expression, case-insensitive	' Thomas ' ~* '. *thomas.* '
!~	Mismatched regular expressions, case-related	' Thomas '!~ '. *thomas.* '
!~*	Mismatched regular expressions, case-insensitive	' Thomas '!~* '. *vadim.* '

Regular Expression quantifier

quantifier	Match
*	A sequence that matches 0 or more atoms
+	A sequence that matches 1 or more atoms
?	A sequence that matches 0 or 1 atoms
{m}	A sequence that exactly matchesmatoms
{m,}	A sequence that matchesmor more atoms
{m,n}	A sequence of atoms that matchesmtoN(containing two ends);mcannot be larger thann
*?	*non-greedy mode
+?	+non-greedy mode
??	?The non-greedy mode
{m}?	Non-greedy mode for{m}
{m,}?	Non-greedy mode for{m,}
{m,n}?	Non-greedy mode for{m,n}

{...The form of the}is called a range . NumbersmandNin a range are unsigned decimal integers, allowing values from 0 to 255 (closed interval).

Regular expression constraints

Constraints	Description
^	Match the beginning of a string
$	Match the end of a string
(? =re)	forward matching of any substring starting point matching there(only in IS)
(?!Re)	Negative lookahead matches any starting point of the substring that does not match there. (Only in IS)

PostgreSQL Regular Expression Query