Oracle Regular Expressions Pocket Reference

Name

( ) (Parentheses) — Defines a subexpression

Synopsis

Place parentheses ( () ) around a portion of a regular expression to define a subexpression. Subexpressions are useful for the following purposes:

• To constrain an alternation to the subexpression.

• To provide for a backreference to the value matched by the subexpression.

• To allow a quantifier to be applied to the subexpression as a whole.

The regular expression in the following example uses parentheses twice. The innermost set constrains the alternation to the three fruit names. The outermost set defines a subexpression in the form of fruit name + space, which we require to appear from 1 to 3 times in the text.

SELECT REGEXP_SUBSTR( 
   'orange apple pear lemon lime',
   'orange ((apple|pear|lemon)[[:space:]]){1,3}')
FROM dual;

orange apple pear lemon

See Section 1.6, especially under Section 1.6.6 and Section 1.6.8, for more examples showing the use of parentheses in regular expressions.