MDEV-7759 NULLIF(x,y) is not equal to CASE WHEN x=y THEN NULL ELSE x END

mysql-test/r/null.result

@@ -502,6 +502,10 @@ NULLIF(TIMESTAMP'2001-01-01 00:00:00',1.0),
 NULLIF(TIMESTAMP'2001-01-01 00:00:00',1e0),
 NULLIF(TIMESTAMP'2001-01-01 00:00:00','2001-01-01'),
 NULLIF(TIMESTAMP'2001-01-01 00:00:00',TIME'00:00:00');
+Warnings:
+Warning	1292	Incorrect datetime value: '1'
+Warning	1292	Incorrect datetime value: '1.0'
+Warning	1292	Incorrect datetime value: '1'
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
@@ -518,6 +522,10 @@ NULLIF(DATE'2001-01-01',1.0),
 NULLIF(DATE'2001-01-01',1e0),
 NULLIF(DATE'2001-01-01','2001-01-01'),
 NULLIF(DATE'2001-01-01',TIME'00:00:00');
+Warnings:
+Warning	1292	Incorrect datetime value: '1'
+Warning	1292	Incorrect datetime value: '1.0'
+Warning	1292	Incorrect datetime value: '1'
 SHOW CREATE TABLE t1;
 Table	Create Table
 t1	CREATE TABLE `t1` (
@@ -1350,5 +1358,37 @@ t2	CREATE TABLE `t2` (
 DROP TABLE t2;
 DROP TABLE t1;
 #
+# MDEV-7759 NULLIF(x,y) is not equal to CASE WHEN x=y THEN NULL ELSE x END
+#
+CREATE TABLE t1 (a YEAR);
+INSERT INTO t1 VALUES (2010),(2020);
+SELECT * FROM t1 WHERE a=2010 AND NULLIF(10.1,a) IS NULL;
+a
+2010
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=2010 AND NULLIF(10.1,a) IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = 2010) and 1)
+SELECT * FROM t1 WHERE a=2010 AND CASE WHEN 10.1=a THEN NULL ELSE 10.1 END IS NULL;
+a
+2010
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=2010 AND CASE WHEN 10.1=a THEN NULL ELSE 10.1 END IS NULL;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	filtered	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	100.00	Using where
+Warnings:
+Note	1003	select `test`.`t1`.`a` AS `a` from `test`.`t1` where ((`test`.`t1`.`a` = 2010) and 1)
+DROP TABLE t1;
+# Two warnings expected
+CREATE TABLE t1 AS SELECT
+NULLIF(TIMESTAMP'2001-01-01 00:00:00',1) AS a,
+CASE WHEN TIMESTAMP'2001-01-01 00:00:00'=1 THEN NULL
+ELSE TIMESTAMP'2001-01-01 00:00:00'
+  END AS b;
+Warnings:
+Warning	1292	Incorrect datetime value: '1'
+Warning	1292	Incorrect datetime value: '1'
+DROP TABLE t1;
+#
 # End of 10.1 tests
 #

mysql-test/t/null.test

@@ -849,6 +849,26 @@ DROP TABLE t2;
 
 DROP TABLE t1;
 
+--echo #
+--echo # MDEV-7759 NULLIF(x,y) is not equal to CASE WHEN x=y THEN NULL ELSE x END
+--echo #
+CREATE TABLE t1 (a YEAR);
+INSERT INTO t1 VALUES (2010),(2020);
+SELECT * FROM t1 WHERE a=2010 AND NULLIF(10.1,a) IS NULL;
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=2010 AND NULLIF(10.1,a) IS NULL;
+SELECT * FROM t1 WHERE a=2010 AND CASE WHEN 10.1=a THEN NULL ELSE 10.1 END IS NULL;
+EXPLAIN EXTENDED SELECT * FROM t1 WHERE a=2010 AND CASE WHEN 10.1=a THEN NULL ELSE 10.1 END IS NULL;
+DROP TABLE t1;
+
+--echo # Two warnings expected
+CREATE TABLE t1 AS SELECT
+  NULLIF(TIMESTAMP'2001-01-01 00:00:00',1) AS a,
+  CASE WHEN TIMESTAMP'2001-01-01 00:00:00'=1 THEN NULL
+       ELSE TIMESTAMP'2001-01-01 00:00:00'
+  END AS b;
+DROP TABLE t1;
+
+
 --echo #
 --echo # End of 10.1 tests
 --echo #

sql/item_cmpfunc.cc

@@ -552,6 +552,26 @@ void Item_func::convert_const_compared_to_int_field(THD *thd)
 }
 
 
+bool Item_func::setup_args_and_comparator(THD *thd, Arg_comparator *cmp)
+{
+  DBUG_ASSERT(arg_count == 2);
+
+  if (args[0]->cmp_type() == STRING_RESULT &&
+      args[1]->cmp_type() == STRING_RESULT &&
+      agg_arg_charsets_for_comparison(cmp->cmp_collation, args, 2))
+      return true;
+
+  args[0]->cmp_context= args[1]->cmp_context=
+    item_cmp_type(args[0]->result_type(), args[1]->result_type());
+
+  //  Convert constants when compared to int/year field, unless this is LIKE
+  if (functype() != LIKE_FUNC)
+    convert_const_compared_to_int_field(thd);
+
+  return cmp->set_cmp_func(this, tmp_arg, tmp_arg + 1, true);
+}
+
+
 void Item_bool_func2::fix_length_and_dec()
 {
   max_length= 1;				     // Function returns 0 or 1
@@ -562,32 +582,7 @@ void Item_bool_func2::fix_length_and_dec()
   */
   if (!args[0] || !args[1])
     return;
-
-  /* 
-    We allow to convert to Unicode character sets in some cases.
-    The conditions when conversion is possible are:
-    - arguments A and B have different charsets
-    - A wins according to coercibility rules
-    - character set of A is superset for character set of B
-   
-    If all of the above is true, then it's possible to convert
-    B into the character set of A, and then compare according
-    to the collation of A.
-  */
-
-  DTCollation coll;
-  if (args[0]->cmp_type() == STRING_RESULT &&
-      args[1]->cmp_type() == STRING_RESULT &&
-      agg_arg_charsets_for_comparison(coll, args, 2))
-    return;
-    
-  args[0]->cmp_context= args[1]->cmp_context=
-    item_cmp_type(args[0]->result_type(), args[1]->result_type());
-
-  //  Convert constants when compared to int/year field, unless this is LIKE
-  if (functype() != LIKE_FUNC)
-    convert_const_compared_to_int_field(current_thd);
-  set_cmp_func();
+  setup_args_and_comparator(current_thd, &cmp);
 }
 
 
@@ -2760,12 +2755,8 @@ Item_func_nullif::fix_length_and_dec()
   decimals= m_args0_copy->decimals;
   unsigned_flag= m_args0_copy->unsigned_flag;
   fix_char_length(m_args0_copy->max_char_length());
-
-  convert_const_compared_to_int_field(current_thd);
-  m_args0_copy->cmp_context= args[1]->cmp_context=
-    item_cmp_type(m_args0_copy->result_type(), args[1]->result_type());
-  cmp.set_cmp_func(this, tmp_arg, tmp_arg + 1, m_args0_copy->cmp_context);
   maybe_null=1;
+  setup_args_and_comparator(current_thd, &cmp);
 }
 
 

sql/item_cmpfunc.h

@@ -66,10 +66,11 @@ class Arg_comparator: public Sql_alloc
   Arg_comparator(Item **a1, Item **a2): a(a1), b(a2),  set_null(TRUE),
     comparators(0), thd(0), a_cache(0), b_cache(0) {};
 
+private:
   int set_cmp_func(Item_result_field *owner_arg,
 			  Item **a1, Item **a2,
 			  Item_result type);
-
+public:
   inline int set_cmp_func(Item_result_field *owner_arg,
 			  Item **a1, Item **a2, bool set_null_arg)
   {

sql/item_func.h

@@ -398,6 +398,15 @@ class Item_func :public Item_result_field
     walk(&Item::call_bool_func_processor, FALSE, (uchar*) &info);
   }
   void convert_const_compared_to_int_field(THD *thd);
+  /**
+    Prepare arguments and setup a comparator.
+    Used in Item_func_xxx with two arguments and a comparator,
+    e.g. Item_bool_func2 and Item_func_nullif.
+    args[0] or args[1] can be modified:
+    - converted to character set and collation of the operation
+    - or replaced to an Item_int_with_ref
+  */
+  bool setup_args_and_comparator(THD *thd, Arg_comparator *cmp);
 };