Fixed bug mdev-11593.

When a condition containing NULLIF is pushed into a materialized
view/derived table the clone of the Item_func_nullif item must
be processed in a special way to guarantee that the first argument
points to the same item as the third argument.

Author: igorbabaev

mysql-test/r/derived_cond_pushdown.result

@@ -8140,3 +8140,41 @@ EXPLAIN
   }
 }
 DROP TABLE t1,t2;
+#
+# MDEV-11593: pushdown of condition with NULLIF
+#
+CREATE TABLE t1 (i INT);
+CREATE OR REPLACE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t1;
+INSERT INTO t1 VALUES (2), (1);
+SELECT * FROM v1 WHERE NULLIF(1, i);
+i
+2
+EXPLAIN FORMAT=JSON
+SELECT * FROM v1 WHERE NULLIF(1, i);
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "<derived2>",
+      "access_type": "ALL",
+      "rows": 2,
+      "filtered": 100,
+      "attached_condition": "nullif(1,v1.i)",
+      "materialized": {
+        "query_block": {
+          "select_id": 2,
+          "table": {
+            "table_name": "t1",
+            "access_type": "ALL",
+            "rows": 2,
+            "filtered": 100,
+            "attached_condition": "nullif(1,t1.i)"
+          }
+        }
+      }
+    }
+  }
+}
+DROP VIEW v1;
+DROP TABLE t1;

mysql-test/t/derived_cond_pushdown.test

@@ -1273,3 +1273,19 @@ SELECT * FROM ( SELECT DISTINCT * FROM t1 ) AS sq
   WHERE i IN ( SELECT MIN(j) FROM t2 );
 
 DROP TABLE t1,t2;
+
+--echo #
+--echo # MDEV-11593: pushdown of condition with NULLIF
+--echo #
+
+CREATE TABLE t1 (i INT);
+CREATE OR REPLACE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t1;
+
+INSERT INTO t1 VALUES (2), (1);
+
+SELECT * FROM v1 WHERE NULLIF(1, i);
+EXPLAIN FORMAT=JSON
+SELECT * FROM v1 WHERE NULLIF(1, i);
+
+DROP VIEW v1;
+DROP TABLE t1;

sql/item_cmpfunc.h

@@ -1070,6 +1070,11 @@ class Item_func_nullif :public Item_func_hybrid_field_type
   */
   Item_cache *m_cache;
   int compare();
+  void reset_first_arg_if_needed()
+  { 
+    if (arg_count == 3 && args[0] != args[2])
+      args[0]= args[2];
+  }
 public:
   /*
     Here we pass three arguments to the parent constructor, as NULLIF
@@ -1120,6 +1125,12 @@ class Item_func_nullif :public Item_func_hybrid_field_type
   }
   Item *get_copy(THD *thd, MEM_ROOT *mem_root)
   { return get_item_copy<Item_func_nullif>(thd, mem_root, this); }
+  Item *derived_field_transformer_for_having(THD *thd, uchar *arg)
+  { reset_first_arg_if_needed(); return this; }
+  Item *derived_field_transformer_for_where(THD *thd, uchar *arg)
+  { reset_first_arg_if_needed(); return this; }
+  Item *derived_grouping_field_transformer_for_where(THD *thd, uchar *arg)
+  { reset_first_arg_if_needed(); return this; }
 };