regexp_extract(string, pattern [,start [,result]])
Return the value that matched a regular expression. When the result parameter is passed, instead of returning the first match, the regexp_extract function will return the Nth match, where N = result.
Example
str = regexp_extract("How much food does a barbarian eat?", "foo|bar")
str = regexp_extract("How much food does a barbarian eat?", "foo|bar", 1, 3)