Grouping Constructs ​

Capturing groups create a sub-expression by placing an expression inside matching open and close parentheses. Quantifiers and optionality can be applied to sub-expressions. Each set of parentheses creates a capture number that is used to identify capturing groups, ranging from 1 to 9 (\1 to \9). Capturing groups can be referenced later by their capture number in the regular expression or the replacement string in REGEXP_REPLACE.

Note: While only 9 can be referenced, Yellowbrick supports patterns that contain up to 16 capturing groups. Using more than 16 capturing groups will result in an error.

Non-capturing groups create a sub-expression without creating a capturing group. Non-capturing groups are indicated by including the question mark ( ? ) and colon ( : ) after the opening parenthesis.

Note: It is recommended that capturing groups not be used when the group is the entire expression as this will only cause the engine to execute slower.

Examples ​

premdb=# select REGEXP_REPLACE('Hello World','(?:\w+) (?:\w+)','\& -> \1') from sys.const;
 regexp_replace  
-----------------
 Hello World -> 
(1 row)

premdb=# select REGEXP_REPLACE('Hello World','(\w+) (?:\w+)','\& -> \1') from sys.const;
   regexp_replace    
----------------------
 Hello World -> Hello
(1 row)

premdb=# select REGEXP_REPLACE('Hello World','(?:\w+) (\w+)','\& -> \1') from sys.const;
   regexp_replace    
----------------------
 Hello World -> World
(1 row)

Parent topic:Regular Expression Details