Fixed bug mdev-10882.

The implementation of the virtual method build_clone for
the class Item_cache was missing.

mysql-test/r/derived_cond_pushdown.result

@@ -7626,3 +7626,65 @@ EXPLAIN
 }
 DROP VIEW v1,v2;
 DROP TABLE t1,t2,t3;
+#
+# MDEV-10882: pushdown of the predicate with cached value
+#
+CREATE TABLE t1 (a INT NOT NULL, b INT NOT NULL) ENGINE=MyISAM;
+CREATE OR REPLACE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t1;
+INSERT INTO t1 VALUES (1,2),(3,4);
+CREATE TABLE t2 (c INT NOT NULL) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (5),(6);
+SELECT a, GROUP_CONCAT(b) FROM v1
+WHERE b IN ( SELECT COUNT(c) FROM t2 ) GROUP BY a;
+a	GROUP_CONCAT(b)
+1	2
+EXPLAIN FORMAT=JSON
+SELECT a, GROUP_CONCAT(b) FROM v1
+WHERE b IN ( SELECT COUNT(c) FROM t2 ) GROUP BY a;
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "<subquery2>",
+      "access_type": "system",
+      "rows": 1,
+      "filtered": 100,
+      "materialized": {
+        "unique": 1,
+        "query_block": {
+          "select_id": 2,
+          "table": {
+            "message": "Select tables optimized away"
+          }
+        }
+      }
+    },
+    "read_sorted_file": {
+      "filesort": {
+        "sort_key": "v1.a",
+        "table": {
+          "table_name": "<derived3>",
+          "access_type": "ALL",
+          "rows": 2,
+          "filtered": 100,
+          "attached_condition": "(v1.b = 2)",
+          "materialized": {
+            "query_block": {
+              "select_id": 3,
+              "table": {
+                "table_name": "t1",
+                "access_type": "ALL",
+                "rows": 2,
+                "filtered": 100,
+                "attached_condition": "(t1.b = 2)"
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+DROP VIEW v1;
+DROP TABLE t1,t2;

mysql-test/t/derived_cond_pushdown.test

@@ -1126,3 +1126,24 @@ SELECT ( SELECT COUNT(*) FROM v2 WHERE s < t2.b ) AS f FROM t2 GROUP BY f;
 
 DROP VIEW v1,v2;
 DROP TABLE t1,t2,t3;
+
+--echo #
+--echo # MDEV-10882: pushdown of the predicate with cached value
+--echo #
+
+CREATE TABLE t1 (a INT NOT NULL, b INT NOT NULL) ENGINE=MyISAM;
+CREATE OR REPLACE ALGORITHM=TEMPTABLE VIEW v1 AS SELECT * FROM t1;
+INSERT INTO t1 VALUES (1,2),(3,4);
+
+CREATE TABLE t2 (c INT NOT NULL) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (5),(6);
+
+SELECT a, GROUP_CONCAT(b) FROM v1
+  WHERE b IN ( SELECT COUNT(c) FROM t2 ) GROUP BY a;
+
+EXPLAIN FORMAT=JSON
+SELECT a, GROUP_CONCAT(b) FROM v1
+  WHERE b IN ( SELECT COUNT(c) FROM t2 ) GROUP BY a;
+
+DROP VIEW v1;
+DROP TABLE t1,t2;

sql/item.h

@@ -5456,6 +5456,15 @@ public:
     example->split_sum_func2(thd, ref_pointer_array, fields, &example, flags);
   }
   Item *get_example() const { return example; }
+  Item* build_clone(THD *thd, MEM_ROOT *mem_root)
+  {
+    Item_cache *copy= (Item_cache *) get_copy(thd, mem_root);
+    if (!copy)
+      return 0;
+    if (!( copy->example= example->build_clone(thd, mem_root)))
+      return 0;
+    return copy;
+  } 
 };