MDEV-29095 REGEXP_REPLACE treats empty strings different than REPLACE in ORACLE mode

Turning REGEXP_REPLACE into two schema-qualified functions:
- mariadb_schema.regexp_replace()
- oracle_schema.regexp_replace()

Fixing oracle_schema.regexp_replace(subj,pattern,replacement) to treat
NULL in "replacement" as an empty string.

Adding new classes implementing oracle_schema.regexp_replace():
- Item_func_regexp_replace_oracle
- Create_func_regexp_replace_oracle

Adding helper methods:
- String *Item::val_str_null_to_empty(String *to)
- String *Item::val_str_null_to_empty(String *to, bool null_to_empty)

and reusing these methods in both Item_func_replace and
Item_func_regexp_replace.

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

@@ -1772,6 +1772,85 @@ Level	Code	Message
 Note	1003	select trim(both ' ' from 'a') AS "oracle_schema.TRIM(BOTH ' ' FROM 'a')"
 Warnings:
 Note	1003	select trim(both ' ' from 'a') AS "oracle_schema.TRIM(BOTH ' ' FROM 'a')"
+CALL p3('REGEXP_REPLACE(''test'',''t'','''')');
+----------
+sql_mode=''   qualifier=''
+query
+EXPLAIN EXTENDED SELECT REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select regexp_replace('test','t','') AS `REGEXP_REPLACE('test','t','')`
+----------
+sql_mode=''   qualifier='unknown_schema.'
+query
+EXPLAIN EXTENDED SELECT unknown_schema.REGEXP_REPLACE('test','t','')
+errmsg
+ERROR: FUNCTION unknown_schema.REGEXP_REPLACE does not exist
+----------
+sql_mode=''   qualifier='mariadb_schema.'
+query
+EXPLAIN EXTENDED SELECT mariadb_schema.REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select regexp_replace('test','t','') AS `mariadb_schema.REGEXP_REPLACE('test','t','')`
+----------
+sql_mode=''   qualifier='maxdb_schema.'
+query
+EXPLAIN EXTENDED SELECT maxdb_schema.REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select regexp_replace('test','t','') AS `maxdb_schema.REGEXP_REPLACE('test','t','')`
+----------
+sql_mode=''   qualifier='oracle_schema.'
+query
+EXPLAIN EXTENDED SELECT oracle_schema.REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select oracle_schema.regexp_replace('test','t','') AS `oracle_schema.REGEXP_REPLACE('test','t','')`
+----------
+sql_mode='ORACLE'   qualifier=''
+query
+EXPLAIN EXTENDED SELECT REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select regexp_replace('test','t','') AS "REGEXP_REPLACE('test','t','')"
+----------
+sql_mode='ORACLE'   qualifier='unknown_schema.'
+query
+EXPLAIN EXTENDED SELECT unknown_schema.REGEXP_REPLACE('test','t','')
+errmsg
+ERROR: FUNCTION unknown_schema.REGEXP_REPLACE does not exist
+----------
+sql_mode='ORACLE'   qualifier='mariadb_schema.'
+query
+EXPLAIN EXTENDED SELECT mariadb_schema.REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select mariadb_schema.regexp_replace('test','t','') AS "mariadb_schema.REGEXP_REPLACE('test','t','')"
+----------
+sql_mode='ORACLE'   qualifier='maxdb_schema.'
+query
+EXPLAIN EXTENDED SELECT maxdb_schema.REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select mariadb_schema.regexp_replace('test','t','') AS "maxdb_schema.REGEXP_REPLACE('test','t','')"
+----------
+sql_mode='ORACLE'   qualifier='oracle_schema.'
+query
+EXPLAIN EXTENDED SELECT oracle_schema.REGEXP_REPLACE('test','t','')
+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
+Level	Code	Message
+Note	1003	select regexp_replace('test','t','') AS "oracle_schema.REGEXP_REPLACE('test','t','')"
+Warnings:
+Note	1003	select regexp_replace('test','t','') AS "oracle_schema.REGEXP_REPLACE('test','t','')"
 CALL p3('CONCAT_OPERATOR_ORACLE(''a'')');
 ----------
 sql_mode=''   qualifier=''

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

+SET sql_mode=ORACLE;
+#
+# MDEV-29095 REGEXP_REPLACE treats empty strings different than REPLACE in ORACLE mode
+#
+CREATE TABLE t1 (replacement VARCHAR(10));
+INSERT INTO t1 VALUES (NULL), ('');
+SELECT replacement, REGEXP_REPLACE('abba','a',replacement) FROM t1 ORDER BY replacement;
+replacement	REGEXP_REPLACE('abba','a',replacement)
+NULL	bb
+	bb
+DROP TABLE t1;
+SELECT REGEXP_REPLACE('abba','a',null);
+REGEXP_REPLACE('abba','a',null)
+bb
+EXPLAIN EXTENDED SELECT REPLACE('abba','a',null) ;
+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
+Warnings:
+Note	1003	select replace('abba','a',NULL) AS "REPLACE('abba','a',null)"
+CREATE VIEW v1 AS SELECT REPLACE('abba','a',null) ;
+SHOW CREATE VIEW v1;
+View	Create View	character_set_client	collation_connection
+v1	CREATE VIEW "v1" AS select replace('abba','a',NULL) AS "REPLACE('abba','a',null)"	latin1	latin1_swedish_ci
+SELECT * FROM v1;
+REPLACE('abba','a',null)
+bb
+SET sql_mode=DEFAULT;
+SHOW CREATE VIEW v1;
+View	Create View	character_set_client	collation_connection
+v1	CREATE ALGORITHM=UNDEFINED DEFINER=`root`@`localhost` SQL SECURITY DEFINER VIEW `v1` AS select oracle_schema.replace('abba','a',NULL) AS `REPLACE('abba','a',null)`	latin1	latin1_swedish_ci
+SELECT * FROM v1;
+REPLACE('abba','a',null)
+bb
+DROP VIEW v1;

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

@@ -165,6 +165,7 @@ CALL p3('TRIM(1,2)');
 CALL p3('TRIM(''a'')');
 CALL p3('TRIM(BOTH '' '' FROM ''a'')');
 
+CALL p3('REGEXP_REPLACE(''test'',''t'','''')');
 
 # Deprecated compatibility XXX_ORACLE functions.
 # These functions are implemented as simple native functions

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

+SET sql_mode=ORACLE;
+
+--echo #
+--echo # MDEV-29095 REGEXP_REPLACE treats empty strings different than REPLACE in ORACLE mode
+--echo #
+
+#SELECT REGEXP_REPLACE(null,'a','b') ;
+#SELECT REGEXP_REPLACE('ab',null,'b') ;
+#SELECT REGEXP_REPLACE('ab','a',null) ;
+#SELECT REGEXP_REPLACE('ab',null,null) ;
+
+CREATE TABLE t1 (replacement VARCHAR(10));
+INSERT INTO t1 VALUES (NULL), ('');
+SELECT replacement, REGEXP_REPLACE('abba','a',replacement) FROM t1 ORDER BY replacement;
+DROP TABLE t1;
+
+SELECT REGEXP_REPLACE('abba','a',null);
+EXPLAIN EXTENDED SELECT REPLACE('abba','a',null) ;
+
+CREATE VIEW v1 AS SELECT REPLACE('abba','a',null) ;
+SHOW CREATE VIEW v1;
+SELECT * FROM v1;
+SET sql_mode=DEFAULT;
+SHOW CREATE VIEW v1;
+SELECT * FROM v1;
+DROP VIEW v1;

sql/item.h

@@ -904,6 +904,19 @@ class Item: public Value_source,
     expressions with subqueries in the ORDER/GROUP clauses.
   */
   String *val_str() { return val_str(&str_value); }
+  String *val_str_null_to_empty(String *to)
+  {
+    String *res= val_str(to);
+    if (res)
+      return res;
+    to->set_charset(collation.collation);
+    to->length(0);
+    return to;
+  }
+  String *val_str_null_to_empty(String *to, bool null_to_empty)
+  {
+    return null_to_empty ? val_str_null_to_empty(to) : val_str(to);
+  }
   virtual Item_func *get_item_func() { return NULL; }
 
   const MY_LOCALE *locale_from_val_str();

sql/item_create.cc

@@ -2666,7 +2666,10 @@ class Create_func_regexp_instr : public Create_func_arg2
 class Create_func_regexp_replace : public Create_func_arg3
 {
 public:
-  virtual Item *create_3_arg(THD *thd, Item *arg1, Item *arg2, Item *arg3);
+  Item *create_3_arg(THD *thd, Item *arg1, Item *arg2, Item *arg3) override
+  {
+    return new (thd->mem_root) Item_func_regexp_replace(thd, arg1, arg2, arg3);
+  }
 
   static Create_func_regexp_replace s_singleton;
 
@@ -2675,6 +2678,28 @@ class Create_func_regexp_replace : public Create_func_arg3
   virtual ~Create_func_regexp_replace() = default;
 };
 
+Create_func_regexp_replace Create_func_regexp_replace::s_singleton;
+
+
+class Create_func_regexp_replace_oracle : public Create_func_arg3
+{
+public:
+  Item *create_3_arg(THD *thd, Item *arg1, Item *arg2, Item *arg3) override
+  {
+    return new (thd->mem_root) Item_func_regexp_replace_oracle(thd, arg1,
+                                                               arg2, arg3);
+  }
+
+  static Create_func_regexp_replace_oracle s_singleton;
+
+protected:
+  Create_func_regexp_replace_oracle() = default;
+  virtual ~Create_func_regexp_replace_oracle() = default;
+};
+
+Create_func_regexp_replace_oracle
+  Create_func_regexp_replace_oracle::s_singleton;
+
 
 class Create_func_regexp_substr : public Create_func_arg2
 {
@@ -6464,15 +6489,6 @@ Create_func_regexp_instr::create_2_arg(THD *thd, Item *arg1, Item *arg2)
 }
 
 
-Create_func_regexp_replace Create_func_regexp_replace::s_singleton;
-
-Item*
-Create_func_regexp_replace::create_3_arg(THD *thd, Item *arg1, Item *arg2, Item *arg3)
-{
-  return new (thd->mem_root) Item_func_regexp_replace(thd, arg1, arg2, arg3);
-}
-
-
 Create_func_regexp_substr Create_func_regexp_substr::s_singleton;
 
 Item*
@@ -7616,6 +7632,8 @@ const Native_func_registry func_array_oracle_overrides[] =
   { { STRING_WITH_LEN("LENGTH") },  BUILDER(Create_func_char_length)},
   { { STRING_WITH_LEN("LPAD") },    BUILDER(Create_func_lpad_oracle)},
   { { STRING_WITH_LEN("LTRIM") },   BUILDER(Create_func_ltrim_oracle)},
+  { { STRING_WITH_LEN("REGEXP_REPLACE") },
+                                    BUILDER(Create_func_regexp_replace_oracle)},
   { { STRING_WITH_LEN("RPAD") },    BUILDER(Create_func_rpad_oracle)},
   { { STRING_WITH_LEN("RTRIM") },   BUILDER(Create_func_rtrim_oracle)},
 

sql/item_strfunc.cc

@@ -1149,8 +1149,7 @@ bool Item_func_reverse::fix_length_and_dec()
     Fix that this works with binary strings when using USE_MB 
 */
 
-String *Item_func_replace::val_str_internal(String *str,
-                                            String *empty_string_for_null)
+String *Item_func_replace::val_str_internal(String *str, bool null_to_empty)
 {
   DBUG_ASSERT(fixed == 1);
   String *res,*res2,*res3;
@@ -1168,13 +1167,8 @@ String *Item_func_replace::val_str_internal(String *str,
   res=args[0]->val_str(str);
   if (args[0]->null_value)
     goto null;
-  res2=args[1]->val_str(&tmp_value);
-  if (args[1]->null_value)
-  {
-    if (!empty_string_for_null)
-      goto null;
-    res2= empty_string_for_null;
-  }
+  if (!(res2= args[1]->val_str_null_to_empty(&tmp_value, null_to_empty)))
+    goto null;
   res->set_charset(collation.collation);
 
 #ifdef USE_MB
@@ -1191,12 +1185,8 @@ String *Item_func_replace::val_str_internal(String *str,
   if (binary_cmp && (offset=res->strstr(*res2)) < 0)
     return res;
 #endif
-  if (!(res3=args[2]->val_str(&tmp_value2)))
-  {
-    if (!empty_string_for_null)
-      goto null;
-    res3= empty_string_for_null;
-  }
+  if (!(res3= args[2]->val_str_null_to_empty(&tmp_value2, null_to_empty)))
+    goto null;
   from_length= res2->length();
   to_length=   res3->length();
 
@@ -1279,7 +1269,7 @@ String *Item_func_replace::val_str_internal(String *str,
     }
     while ((offset=res->strstr(*res2,(uint) offset)) >= 0);
   }
-  if (empty_string_for_null && !res->length())
+  if (null_to_empty && !res->length())
     goto null;
 
   return res;
@@ -1385,20 +1375,22 @@ bool Item_func_regexp_replace::append_replacement(String *str,
 }
 
 
-String *Item_func_regexp_replace::val_str(String *str)
+String *Item_func_regexp_replace::val_str_internal(String *str,
+                                                   bool null_to_empty)
 {
   DBUG_ASSERT(fixed == 1);
   char buff0[MAX_FIELD_WIDTH];
   char buff2[MAX_FIELD_WIDTH];
   String tmp0(buff0,sizeof(buff0),&my_charset_bin);
   String tmp2(buff2,sizeof(buff2),&my_charset_bin);
-  String *source= args[0]->val_str(&tmp0);
-  String *replace= args[2]->val_str(&tmp2);
+  String *source, *replace;
   LEX_CSTRING src, rpl;
   int startoffset= 0;
 
-  if ((null_value= (args[0]->null_value || args[2]->null_value ||
-                    re.recompile(args[1]))))
+  if ((null_value=
+        (!(source= args[0]->val_str(&tmp0)) ||
+         !(replace= args[2]->val_str_null_to_empty(&tmp2, null_to_empty)) ||
+         re.recompile(args[1]))))
     return (String *) 0;
 
   if (!(source= re.convert_if_needed(source, &re.subject_converter)) ||

sql/item_strfunc.h

@@ -353,12 +353,13 @@ class Item_func_reverse :public Item_str_func
 class Item_func_replace :public Item_str_func
 {
   String tmp_value,tmp_value2;
+protected:
+  String *val_str_internal(String *str, bool null_to_empty);
 public:
   Item_func_replace(THD *thd, Item *org, Item *find, Item *replace):
     Item_str_func(thd, org, find, replace) {}
-  String *val_str(String *to) { return val_str_internal(to, NULL); };
+  String *val_str(String *to) { return val_str_internal(to, false); };
   bool fix_length_and_dec();
-  String *val_str_internal(String *str, String *empty_string_for_null);
   const Schema *schema() const { return &mariadb_schema; }
   void print(String *str, enum_query_type query_type)
   {
@@ -377,7 +378,7 @@ class Item_func_replace_oracle :public Item_func_replace
 public:
   Item_func_replace_oracle(THD *thd, Item *org, Item *find, Item *replace):
     Item_func_replace(thd, org, find, replace) {}
-  String *val_str(String *to) { return val_str_internal(to, &tmp_emtpystr); };
+  String *val_str(String *to) { return val_str_internal(to, true); };
   const Schema *schema() const { return &oracle_schema_ref; }
   void print(String *str, enum_query_type query_type)
   {
@@ -401,10 +402,18 @@ class Item_func_regexp_replace :public Item_str_func
   bool append_replacement(String *str,
                           const LEX_CSTRING *source,
                           const LEX_CSTRING *replace);
+protected:
+  String *val_str_internal(String *str, bool null_to_empty);
 public:
   Item_func_regexp_replace(THD *thd, Item *a, Item *b, Item *c):
     Item_str_func(thd, a, b, c)
     {}
+  const Schema *schema() const { return &mariadb_schema; }
+  void print(String *str, enum_query_type query_type)
+  {
+    print_sql_mode_qualified_name(str, query_type);
+    print_args_parenthesized(str, query_type);
+  }
   void cleanup()
   {
     DBUG_ENTER("Item_func_regex::cleanup");
@@ -412,7 +421,10 @@ class Item_func_regexp_replace :public Item_str_func
     re.cleanup();
     DBUG_VOID_RETURN;
   }
-  String *val_str(String *str);
+  String *val_str(String *str)
+  {
+    return val_str_internal(str, false);
+  }
   bool fix_fields(THD *thd, Item **ref);
   bool fix_length_and_dec();
   const char *func_name() const { return "regexp_replace"; }
@@ -420,6 +432,26 @@ class Item_func_regexp_replace :public Item_str_func
 };
 
 
+class Item_func_regexp_replace_oracle: public Item_func_regexp_replace
+{
+public:
+  Item_func_regexp_replace_oracle(THD *thd, Item *a, Item *b, Item *c)
+   :Item_func_regexp_replace(thd, a, b, c)
+  {}
+  const Schema *schema() const { return &oracle_schema_ref; }
+  bool fix_length_and_dec()
+  {
+    bool rc= Item_func_regexp_replace::fix_length_and_dec();
+    maybe_null= true; // Empty result is converted to NULL
+    return rc;
+  }
+  String *val_str(String *str)
+  {
+    return val_str_internal(str, true);
+  }
+};
+
+
 class Item_func_regexp_substr :public Item_str_func
 {
   Regexp_processor_pcre re;