Fixed the bug mdev-13193.

When an equality that can be pushed into a materialized derived
table / view is extracted from multiple equalities and their
operands are cloned then if they have some pointers to Item_equal
objects those pointers must be set to NULL in the clones. Anyway
they are not valid in the pushed predicates.

mysql-test/r/derived_cond_pushdown.result

@@ -8709,3 +8709,60 @@ EXPLAIN
 }
 DROP VIEW v1;
 DROP TABLE t1;
+#
+# MDEV-13193: pushdown of equality extracted from multiple equality
+#
+CREATE TABLE t1 (i1 int, KEY(i1)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1),(2);
+CREATE TABLE t2 (i2 int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (2),(4);
+CREATE ALGORITHM=TEMPTABLE VIEW v2 AS SELECT * FROM t2;
+SELECT * FROM t1, ( SELECT * FROM v2 ) AS sq
+WHERE i1 = 1 AND ( i1 = i2 OR i1 = 2 );
+i1	i2
+explain format=json SELECT * FROM t1, ( SELECT * FROM v2 ) AS sq
+WHERE i1 = 1 AND ( i1 = i2 OR i1 = 2 );
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "t1",
+      "access_type": "ref",
+      "possible_keys": ["i1"],
+      "key": "i1",
+      "key_length": "5",
+      "used_key_parts": ["i1"],
+      "ref": ["const"],
+      "rows": 1,
+      "filtered": 100,
+      "using_index": true
+    },
+    "block-nl-join": {
+      "table": {
+        "table_name": "<derived3>",
+        "access_type": "ALL",
+        "rows": 2,
+        "filtered": 100,
+        "attached_condition": "v2.i2 = 1"
+      },
+      "buffer_type": "flat",
+      "buffer_size": "256Kb",
+      "join_type": "BNL",
+      "materialized": {
+        "query_block": {
+          "select_id": 3,
+          "table": {
+            "table_name": "t2",
+            "access_type": "ALL",
+            "rows": 2,
+            "filtered": 100,
+            "attached_condition": "t2.i2 = 1"
+          }
+        }
+      }
+    }
+  }
+}
+DROP VIEW v2;
+DROP TABLE t1,t2;

mysql-test/r/derived_view.result

@@ -1107,7 +1107,7 @@ id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t1	system	NULL	NULL	NULL	NULL	1	
 1	PRIMARY	t2	ref	a	a	4	const	1	Using index
 1	PRIMARY	<derived2>	ref	key0	key0	8	const,const	1	
-2	DERIVED	t3	ALL	NULL	NULL	NULL	NULL	12	Using where; Using temporary; Using filesort
+2	DERIVED	t3	ALL	NULL	NULL	NULL	NULL	12	Using temporary; Using filesort
 SELECT * FROM t1, t2, v1 WHERE t2.a=t1.a AND t2.a=v1.a AND t2.a=v1.b;
 a	a	a	b
 c	c	c	c

mysql-test/t/derived_cond_pushdown.test

@@ -1526,3 +1526,25 @@ eval explain format=json $q;
 
 DROP VIEW v1;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-13193: pushdown of equality extracted from multiple equality
+--echo #
+
+CREATE TABLE t1 (i1 int, KEY(i1)) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (1),(2);
+
+CREATE TABLE t2 (i2 int) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (2),(4);
+
+CREATE ALGORITHM=TEMPTABLE VIEW v2 AS SELECT * FROM t2;
+
+let $q=
+SELECT * FROM t1, ( SELECT * FROM v2 ) AS sq
+  WHERE i1 = 1 AND ( i1 = i2 OR i1 = 2 );
+
+eval $q;
+eval explain format=json $q;
+
+DROP VIEW v2;
+DROP TABLE t1,t2;

sql/table.cc

@@ -8237,8 +8237,12 @@ Item* TABLE_LIST::build_pushable_cond_for_table(THD *thd, Item *cond)
       Item *left_item_clone= left_item->build_clone(thd, thd->mem_root);
       Item *right_item_clone= item->build_clone(thd, thd->mem_root);
       if (left_item_clone && right_item_clone)
+      {
+        left_item_clone->set_item_equal(NULL);
+        right_item_clone->set_item_equal(NULL);
 	eq= new (thd->mem_root) Item_func_eq(thd, right_item_clone,
                                          left_item_clone);
+      }
       if (eq)
       {
 	i++;