Add the support of 'SUBSTR' function compatible with Oracle and SAPDB (SCRUM #872)

sql/lex.h:
  Add SUBSTR aliased to SUBSTRING
sql/item_strfunc.cc:
  Implement SUBSTR negative offset
mysql-test/t/func_str.test:
  New tests for SUBSTR
mysql-test/r/func_str.result:
  Updated SUBSTR results

mysql-test/r/func_str.result

@@ -532,3 +532,24 @@ t1	CREATE TABLE `t1` (
   `replace(_latin2'abcd',_latin2'b',_latin2'B')` char(4) character set latin2 NOT NULL default ''
 ) TYPE=MyISAM CHARSET=latin1
 drop table t1;
+select SUBSTR('abcdefg',3,2);
+SUBSTR('abcdefg',3,2)
+cd
+select SUBSTRING('abcdefg',3,2);
+SUBSTRING('abcdefg',3,2)
+cd
+select SUBSTR('abcdefg',-3,2) FROM DUAL;
+SUBSTR('abcdefg',-3,2)
+ef
+select SUBSTR('abcdefg',-1,5) FROM DUAL;
+SUBSTR('abcdefg',-1,5)
+g
+select SUBSTR('abcdefg',0,0) FROM DUAL;
+SUBSTR('abcdefg',0,0)
+
+select SUBSTR('abcdefg',-1,-1) FROM DUAL;
+SUBSTR('abcdefg',-1,-1)
+
+select SUBSTR('abcdefg',1,-1) FROM DUAL;
+SUBSTR('abcdefg',1,-1)
+

mysql-test/t/func_str.test

@@ -294,3 +294,14 @@ select
 ;
 show create table t1;
 drop table t1;
+
+#
+# test for SUBSTR
+#
+select SUBSTR('abcdefg',3,2);
+select SUBSTRING('abcdefg',3,2);
+select SUBSTR('abcdefg',-3,2) FROM DUAL;
+select SUBSTR('abcdefg',-1,5) FROM DUAL;
+select SUBSTR('abcdefg',0,0) FROM DUAL;
+select SUBSTR('abcdefg',-1,-1) FROM DUAL;
+select SUBSTR('abcdefg',1,-1) FROM DUAL;

sql/item_strfunc.cc

@@ -979,13 +979,14 @@ void Item_func_right::fix_length_and_dec()
 String *Item_func_substr::val_str(String *str)
 {
   String *res  = args[0]->val_str(str);
-  int32 start	= (int32) args[1]->val_int()-1;
+  int32 start	= (int32) args[1]->val_int();
   int32 length	= arg_count == 3 ? (int32) args[2]->val_int() : INT_MAX32;
   int32 tmp_length;
 
   if ((null_value=(args[0]->null_value || args[1]->null_value ||
 		   (arg_count == 3 && args[2]->null_value))))
     return 0; /* purecov: inspected */
+  start= (int32)((start < 0) ? res->length() + start : start -1);
   start=res->charpos(start);
   length=res->charpos(length,start);
   if (start < 0 || (uint) start+1 > res->length() || length <= 0)

sql/lex.h

@@ -627,6 +627,7 @@ static SYMBOL sql_functions[] = {
   { "STD",		SYM(STD_SYM),0,0},
   { "STDDEV",		SYM(STD_SYM),0,0},
   { "STRCMP",		SYM(FUNC_ARG2),0,CREATE_FUNC(create_func_strcmp)},
+  { "SUBSTR",	  	SYM(SUBSTRING),0,0},
   { "SUBSTRING",	SYM(SUBSTRING),0,0},
   { "SUBSTRING_INDEX",	SYM(SUBSTRING_INDEX),0,0},
   { "SUBTIME",          SYM(FUNC_ARG2),0,CREATE_FUNC(create_func_subtime)},