Implement regexp_match(), a simplified alternative to regexp_matches().

regexp_match() is like regexp_matches(), but it disallows the 'g' flag
and in consequence does not need to return a set.  Instead, it returns
a simple text array value, or NULL if there's no match.  Previously people
usually got that behavior with a sub-select, but this way is considerably
more efficient.

Documentation adjusted so that regexp_match() is presented first and then
regexp_matches() is introduced as a more complicated version.  This is
a bit historically revisionist but seems pedagogically better.

Still TODO: extend contrib/citext to support this function.

Emre Hasegeli, reviewed by David Johnston

Discussion: <CAE2gYzy42sna2ME_e3y1KLQ-4UBrB-eVF0SWn8QG39sQSeVhEw@mail.gmail.com>

3 files changed, 9 insertions, 3 deletions

diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h
index 82810c8fbae..fb356bf3cd8 100644
--- a/src/include/catalog/catversion.h
+++ b/src/include/catalog/catversion.h
@@ -53,6 +53,6 @@
  */
 
 /*							yyyymmddN */
-#define CATALOG_VERSION_NO	201608161
+#define CATALOG_VERSION_NO	201608171
 
 #endif
diff --git a/src/include/catalog/pg_proc.h b/src/include/catalog/pg_proc.h
index af19c1a82b6..6fed7a0d198 100644
--- a/src/include/catalog/pg_proc.h
+++ b/src/include/catalog/pg_proc.h
@@ -1912,10 +1912,14 @@ DATA(insert OID =  2284 ( regexp_replace	   PGNSP PGUID 12 1 0 0 0 f f f f t f i
 DESCR("replace text using regexp");
 DATA(insert OID =  2285 ( regexp_replace	   PGNSP PGUID 12 1 0 0 0 f f f f t f i s 4 0 25 "25 25 25 25" _null_ _null_ _null_ _null_ _null_ textregexreplace _null_ _null_ _null_ ));
 DESCR("replace text using regexp");
+DATA(insert OID =  3396 ( regexp_match	   PGNSP PGUID 12 1 0 0 0 f f f f t f i s 2 0 1009 "25 25" _null_ _null_ _null_ _null_ _null_ regexp_match_no_flags _null_ _null_ _null_ ));
+DESCR("find first match for regexp");
+DATA(insert OID =  3397 ( regexp_match	   PGNSP PGUID 12 1 0 0 0 f f f f t f i s 3 0 1009 "25 25 25" _null_ _null_ _null_ _null_ _null_ regexp_match _null_ _null_ _null_ ));
+DESCR("find first match for regexp");
 DATA(insert OID =  2763 ( regexp_matches   PGNSP PGUID 12 1 1 0 0 f f f f t t i s 2 0 1009 "25 25" _null_ _null_ _null_ _null_ _null_ regexp_matches_no_flags _null_ _null_ _null_ ));
-DESCR("find all match groups for regexp");
+DESCR("find match(es) for regexp");
 DATA(insert OID =  2764 ( regexp_matches   PGNSP PGUID 12 1 10 0 0 f f f f t t i s 3 0 1009 "25 25 25" _null_ _null_ _null_ _null_ _null_ regexp_matches _null_ _null_ _null_ ));
-DESCR("find all match groups for regexp");
+DESCR("find match(es) for regexp");
 DATA(insert OID =  2088 ( split_part   PGNSP PGUID 12 1 0 0 0 f f f f t f i s 3 0 25 "25 25 23" _null_ _null_ _null_ _null_ _null_	split_text _null_ _null_ _null_ ));
 DESCR("split string by field_sep and return field_num");
 DATA(insert OID =  2765 ( regexp_split_to_table PGNSP PGUID 12 1 1000 0 0 f f f f t t i s 2 0 25 "25 25" _null_ _null_ _null_ _null_ _null_ regexp_split_to_table_no_flags _null_ _null_ _null_ ));
diff --git a/src/include/utils/builtins.h b/src/include/utils/builtins.h
index a91be981b98..40e25c88247 100644
--- a/src/include/utils/builtins.h
+++ b/src/include/utils/builtins.h
@@ -628,6 +628,8 @@ extern Datum textregexsubstr(PG_FUNCTION_ARGS);
 extern Datum textregexreplace_noopt(PG_FUNCTION_ARGS);
 extern Datum textregexreplace(PG_FUNCTION_ARGS);
 extern Datum similar_escape(PG_FUNCTION_ARGS);
+extern Datum regexp_match(PG_FUNCTION_ARGS);
+extern Datum regexp_match_no_flags(PG_FUNCTION_ARGS);
 extern Datum regexp_matches(PG_FUNCTION_ARGS);
 extern Datum regexp_matches_no_flags(PG_FUNCTION_ARGS);
 extern Datum regexp_split_to_table(PG_FUNCTION_ARGS);