Implement SQL99 OVERLAY(). Allows substitution of a substring in a string.

Implement SQL99 SIMILAR TO as a synonym for our existing operator "~".
Implement SQL99 regular expression SUBSTRING(string FROM pat FOR escape).
 Extend the definition to make the FOR clause optional.
 Define textregexsubstr() to actually implement this feature.
Update the regression test to include these new string features.
 All tests pass.
Rename the regular expression support routines from "pg95_xxx" to "pg_xxx".
Define CREATE CHARACTER SET in the parser per SQL99. No implementation yet.

src/test/regress/sql/strings.sql

@@ -4,6 +4,7 @@
 --
 
 -- SQL92 string continuation syntax
+-- E021-03 character string literals
 SELECT 'first line'
 ' - next line'
 	' - third line'
@@ -17,6 +18,7 @@ SELECT 'first line'
 
 --
 -- test conversions between various string types
+-- E021-10 implicit casting among the character data types
 --
 
 SELECT CAST(f1 AS text) AS "text(char)" FROM CHAR_TBL;
@@ -41,8 +43,10 @@ SELECT CAST(name 'namefield' AS varchar) AS "varchar(name)";
 
 --
 -- test SQL92 string functions
+-- E### and T### are feature reference numbers from SQL99
 --
 
+-- E021-09 trim function
 SELECT TRIM(BOTH FROM '  bunch o blanks  ') = 'bunch o blanks' AS "bunch o blanks";
 
 SELECT TRIM(LEADING FROM '  bunch o blanks  ') = 'bunch o blanks  ' AS "bunch o blanks  ";
@@ -51,20 +55,46 @@ SELECT TRIM(TRAILING FROM '  bunch o blanks  ') = '  bunch o blanks' AS "  bunch
 
 SELECT TRIM(BOTH 'x' FROM 'xxxxxsome Xsxxxxx') = 'some Xs' AS "some Xs";
 
+-- E021-06 substring expression
 SELECT SUBSTRING('1234567890' FROM 3) = '34567890' AS "34567890";
 
 SELECT SUBSTRING('1234567890' FROM 4 FOR 3) = '456' AS "456";
 
+-- T581 regular expression substring
+SELECT SUBSTRING('abcdefg' FROM '(b|f).*(d)' FOR '#') AS "bcd";
+
+-- No match should return NULL
+SELECT SUBSTRING('abcdefg' FROM '(1|2|3)' FOR '#') IS NULL AS "True";
+
+-- Null inputs should return NULL
+SELECT SUBSTRING('abcdefg' FROM '(b|c)' FOR NULL) IS NULL AS "True";
+SELECT SUBSTRING(NULL FROM '(b|c)' FOR '#') IS NULL AS "True";
+SELECT SUBSTRING('abcdefg' FROM NULL FOR '#') IS NULL AS "True";
+
+-- PostgreSQL extention to allow omitting the escape character
+SELECT SUBSTRING('abcdefg' FROM '(c|d).e') AS "cde";
+
+-- E021-11 position expression
 SELECT POSITION('4' IN '1234567890') = '4' AS "4";
 
 SELECT POSITION(5 IN '1234567890') = '5' AS "5";
 
+-- T312 character overlay function
+SELECT OVERLAY('abcdef' PLACING '45' FROM 4) AS "abc45f";
+
+SELECT OVERLAY('yabadoo' PLACING 'daba' FROM 5) AS "yabadaba";
+
+SELECT OVERLAY('yabadoo' PLACING 'daba' FROM 5 FOR 0) AS "yabadabadoo";
+
+SELECT OVERLAY('babosa' PLACING 'ubb' FROM 2 FOR 4) AS "bubba";
+
 --
 -- test LIKE
 -- Be sure to form every test as a LIKE/NOT LIKE pair.
 --
 
 -- simplest examples
+-- E061-04 like predicate
 SELECT 'hawkeye' LIKE 'h%' AS "true";
 SELECT 'hawkeye' NOT LIKE 'h%' AS "false";
 
@@ -94,6 +124,7 @@ SELECT 'indio' LIKE 'ind_o' ESCAPE '$' AS "true";
 SELECT 'indio' NOT LIKE 'ind_o' ESCAPE '$' AS "false";
 
 -- escape character
+-- E061-05 like predicate with escape clause
 SELECT 'h%' LIKE 'h#%' ESCAPE '#' AS "true";
 SELECT 'h%' NOT LIKE 'h#%' ESCAPE '#' AS "false";
 
@@ -156,6 +187,7 @@ SELECT 'Hawkeye' NOT ILIKE 'h%' AS "false";
 -- test implicit type conversion
 --
 
+-- E021-07 character concatenation
 SELECT 'unknown' || ' and unknown' AS "Concat unknown types";
 
 SELECT text 'text' || ' and unknown' AS "Concat text to unknown type";
@@ -165,4 +197,3 @@ SELECT char(20) 'characters' || 'and text' AS "Concat char to unknown type";
 SELECT text 'text' || char(20) ' and characters' AS "Concat text to char";
 
 SELECT text 'text' || varchar ' and varchar' AS "Concat text to varchar";
-