MDEV-10574 / SUBSTR - sql_mode=Oracle: return null instead of empty string

mysql-test/suite/compat/oracle/r/func_substr.result

+#
+# MDEV-14012 - sql_mode=Oracle: substr(): treat position 0 as position 1
+# MDEV-10574 - sql_mode=Oracle: return null instead of empty string
+#
 SET sql_mode=ORACLE;
 SELECT SUBSTR('abc',2,1),SUBSTR('abc',1,1), SUBSTR('abc',0,1) FROM dual;
 SUBSTR('abc',2,1)	SUBSTR('abc',1,1)	SUBSTR('abc',0,1)
@@ -22,19 +26,52 @@ SUBSTR('abc',2,null)	SUBSTR('abc',1,null)	SUBSTR('abc',0,null)
 NULL	NULL	NULL
 SELECT SUBSTR('abc',2,0),SUBSTR('abc',1,0), SUBSTR('abc',0,0) FROM dual;
 SUBSTR('abc',2,0)	SUBSTR('abc',1,0)	SUBSTR('abc',0,0)
-		
-create table t1 (c1 varchar(10),start integer, length integer);
+NULL	NULL	NULL
+SELECT SUBSTR('abc',2,-1),SUBSTR('abc',1,-1), SUBSTR('abc',0,-1) FROM dual;
+SUBSTR('abc',2,-1)	SUBSTR('abc',1,-1)	SUBSTR('abc',0,-1)
+NULL	NULL	NULL
+SELECT SUBSTR(SPACE(0),1) FROM DUAL;
+SUBSTR(SPACE(0),1)
+NULL
+CREATE TABLE t1 (c1 VARCHAR(10),start INTEGER, length INTEGER);
 INSERT INTO t1 VALUES ('abc', 1, 1);
 INSERT INTO t1 VALUES ('abc', 0, 1);
 INSERT INTO t1 VALUES (null, 1, 1);
 INSERT INTO t1 VALUES (null, 0, 1);
-select substr(c1,start,length) from t1;
-substr(c1,start,length)
+INSERT INTO t1 VALUES ('abc', 1, 0);
+INSERT INTO t1 VALUES ('abc', 0, 0);
+INSERT INTO t1 VALUES (null, 1, 0);
+INSERT INTO t1 VALUES (null, 0, 0);
+INSERT INTO t1 VALUES ('abc', 1, -1);
+INSERT INTO t1 VALUES ('abc', 0, -1);
+INSERT INTO t1 VALUES (null, 1, -1);
+INSERT INTO t1 VALUES (null, 0, -1);
+INSERT INTO t1 VALUES (SPACE(0), 0, 1);
+SELECT SUBSTR(c1,start,length) FROM t1;
+SUBSTR(c1,start,length)
 a
 a
 NULL
 NULL
-drop table t1;
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+NULL
+DROP TABLE t1;
+CREATE TABLE t1 (c1 VARCHAR(10) NOT NULL);
+CREATE TABLE t2 AS SELECT SUBSTR(C1,1,1) AS C1 from t1;
+SHOW CREATE TABLE t2;
+Table	Create Table
+t2	CREATE TABLE "t2" (
+  "C1" varchar(1) DEFAULT NULL
+)
+DROP TABLE t2;
+DROP TABLE t1;
 EXPLAIN EXTENDED SELECT SUBSTR('abc',2,1) ;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
 1	SIMPLE	NULL	NULL	NULL	NULL	NULL	NULL	NULL	NULL	No tables used

mysql-test/suite/compat/oracle/t/func_substr.test

-#
-# MDEV-14012 - sql_mode=Oracle: substr(): treat position 0 as position 1
-#
+--echo #
+--echo # MDEV-14012 - sql_mode=Oracle: substr(): treat position 0 as position 1
+--echo # MDEV-10574 - sql_mode=Oracle: return null instead of empty string
+--echo #
 
 SET sql_mode=ORACLE;
 SELECT SUBSTR('abc',2,1),SUBSTR('abc',1,1), SUBSTR('abc',0,1) FROM dual;
@@ -11,14 +12,32 @@ SELECT SUBSTR('abc',-2,1),SUBSTR('abc',-1,1), SUBSTR('abc',-0,1) FROM dual;
 SELECT SUBSTR('abc',null) FROM dual;
 SELECT SUBSTR('abc',2,null),SUBSTR('abc',1,null), SUBSTR('abc',0,null) FROM dual;
 SELECT SUBSTR('abc',2,0),SUBSTR('abc',1,0), SUBSTR('abc',0,0) FROM dual;
+SELECT SUBSTR('abc',2,-1),SUBSTR('abc',1,-1), SUBSTR('abc',0,-1) FROM dual;
+SELECT SUBSTR(SPACE(0),1) FROM DUAL;
 
-create table t1 (c1 varchar(10),start integer, length integer);
+CREATE TABLE t1 (c1 VARCHAR(10),start INTEGER, length INTEGER);
 INSERT INTO t1 VALUES ('abc', 1, 1);
 INSERT INTO t1 VALUES ('abc', 0, 1);
 INSERT INTO t1 VALUES (null, 1, 1);
 INSERT INTO t1 VALUES (null, 0, 1);
-select substr(c1,start,length) from t1;
-drop table t1;
+INSERT INTO t1 VALUES ('abc', 1, 0);
+INSERT INTO t1 VALUES ('abc', 0, 0);
+INSERT INTO t1 VALUES (null, 1, 0);
+INSERT INTO t1 VALUES (null, 0, 0);
+INSERT INTO t1 VALUES ('abc', 1, -1);
+INSERT INTO t1 VALUES ('abc', 0, -1);
+INSERT INTO t1 VALUES (null, 1, -1);
+INSERT INTO t1 VALUES (null, 0, -1);
+INSERT INTO t1 VALUES (SPACE(0), 0, 1);
+
+SELECT SUBSTR(c1,start,length) FROM t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 (c1 VARCHAR(10) NOT NULL);
+CREATE TABLE t2 AS SELECT SUBSTR(C1,1,1) AS C1 from t1;
+SHOW CREATE TABLE t2;
+DROP TABLE t2;
+DROP TABLE t1;
 
 EXPLAIN EXTENDED SELECT SUBSTR('abc',2,1) ;
 

sql/item_strfunc.h

@@ -35,7 +35,7 @@ class Item_str_func :public Item_func
      character set. No memory is allocated.
      @retval A pointer to the str_value member.
    */
-  String *make_empty_result()
+  virtual String *make_empty_result()
   {
     /*
       Reset string length to an empty string. We don't use str_value.set() as
@@ -500,11 +500,18 @@ class Item_func_substr_oracle :public Item_func_substr
 protected:
   longlong get_position()
   { longlong pos= args[1]->val_int(); return pos == 0 ? 1 : pos; }
+  String *make_empty_result()
+  { null_value= 1; return NULL; }
 public:
   Item_func_substr_oracle(THD *thd, Item *a, Item *b):
     Item_func_substr(thd, a, b) {}
   Item_func_substr_oracle(THD *thd, Item *a, Item *b, Item *c):
     Item_func_substr(thd, a, b, c) {}
+  void fix_length_and_dec()
+  {
+    Item_func_substr::fix_length_and_dec();
+    maybe_null= true;
+  }
   const char *func_name() const { return "substr_oracle"; }
   Item *get_copy(THD *thd, MEM_ROOT *mem_root)
   { return get_item_copy<Item_func_substr_oracle>(thd, mem_root, this); }