MDEV-16765: Missing rows with pushdown condition defined with CASE us…

…ing Item_cond

The bug appears because of the wrong pushdown into the WHERE clause of the
materialized derived table/view work. For the excl_dep_on_grouping_fields()
method that checks if the condition can be pushed into the WHERE clause
the case when Item_cond is used is missing. For Item_cond elements this
method always returns positive result (that condition can be pushed).
So this condition is pushed even if is shouldn't be pushed.

To fix it new Item_cond::excl_dep_on_grouping_fields() method is added.

mysql-test/r/derived_cond_pushdown.result

@@ -10017,3 +10017,206 @@ a
 7
 4
 DROP TABLE t1,t2,t3;
+#
+# MDEV-16765: pushdown condition with the CASE structure
+#             defined with Item_cond item
+#
+CREATE TABLE t1(a INT, b INT);
+INSERT INTO t1 VALUES (1,2), (3,4), (2,3);
+SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.max_a=1) OR (tab2.max_a=2))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+max_a	b
+1	2
+1	3
+EXPLAIN FORMAT=JSON SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.max_a=1) OR (tab2.max_a=2))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "<derived3>",
+      "access_type": "ALL",
+      "rows": 3,
+      "filtered": 100,
+      "attached_condition": "case when (tab2.max_a = 1 or tab2.max_a = 2) then 1 else 0 end = 1",
+      "materialized": {
+        "query_block": {
+          "select_id": 3,
+          "having_condition": "case when (max_a = 1 or max_a = 2) then 1 else 0 end = 1",
+          "filesort": {
+            "sort_key": "t1.b",
+            "temporary_table": {
+              "table": {
+                "table_name": "t1",
+                "access_type": "ALL",
+                "rows": 3,
+                "filtered": 100
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.max_a=1) OR ((tab2.max_a>2) AND (tab2.max_a<4)))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+max_a	b
+1	2
+1	4
+EXPLAIN FORMAT=JSON SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.max_a=1) OR ((tab2.max_a>2) AND (tab2.max_a<4)))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "<derived3>",
+      "access_type": "ALL",
+      "rows": 3,
+      "filtered": 100,
+      "attached_condition": "case when (tab2.max_a = 1 or tab2.max_a > 2 and tab2.max_a < 4) then 1 else 0 end = 1",
+      "materialized": {
+        "query_block": {
+          "select_id": 3,
+          "having_condition": "case when (max_a = 1 or max_a > 2 and max_a < 4) then 1 else 0 end = 1",
+          "filesort": {
+            "sort_key": "t1.b",
+            "temporary_table": {
+              "table": {
+                "table_name": "t1",
+                "access_type": "ALL",
+                "rows": 3,
+                "filtered": 100
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.max_a>1) AND ((tab2.max_a=2) OR (tab2.max_a>2)))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+max_a	b
+1	3
+1	4
+EXPLAIN FORMAT=JSON SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.max_a>1) AND ((tab2.max_a=2) OR (tab2.max_a>2)))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "<derived3>",
+      "access_type": "ALL",
+      "rows": 3,
+      "filtered": 100,
+      "attached_condition": "case when (tab2.max_a > 1 and (tab2.max_a = 2 or tab2.max_a > 2)) then 1 else 0 end = 1",
+      "materialized": {
+        "query_block": {
+          "select_id": 3,
+          "having_condition": "case when (max_a > 1 and (max_a = 2 or max_a > 2)) then 1 else 0 end = 1",
+          "filesort": {
+            "sort_key": "t1.b",
+            "temporary_table": {
+              "table": {
+                "table_name": "t1",
+                "access_type": "ALL",
+                "rows": 3,
+                "filtered": 100
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.b=2) OR (tab2.b=4))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+max_a	b
+1	2
+1	4
+EXPLAIN FORMAT=JSON SELECT *
+FROM
+(
+SELECT CASE WHEN ((tab2.b=2) OR (tab2.b=4))
+THEN 1 ELSE 0 END AS max_a,b
+FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EXPLAIN
+{
+  "query_block": {
+    "select_id": 1,
+    "table": {
+      "table_name": "<derived3>",
+      "access_type": "ALL",
+      "rows": 3,
+      "filtered": 100,
+      "attached_condition": "case when (tab2.b = 2 or tab2.b = 4) then 1 else 0 end = 1",
+      "materialized": {
+        "query_block": {
+          "select_id": 3,
+          "filesort": {
+            "sort_key": "t1.b",
+            "temporary_table": {
+              "table": {
+                "table_name": "t1",
+                "access_type": "ALL",
+                "rows": 3,
+                "filtered": 100,
+                "attached_condition": "case when (t1.b = 2 or t1.b = 4) then 1 else 0 end = 1"
+              }
+            }
+          }
+        }
+      }
+    }
+  }
+}
+DROP TABLE t1;

mysql-test/t/derived_cond_pushdown.test

@@ -1964,3 +1964,61 @@ eval $q3;
 SELECT * FROM t2;
 
 DROP TABLE t1,t2,t3;
+
+--echo #
+--echo # MDEV-16765: pushdown condition with the CASE structure
+--echo #             defined with Item_cond item
+--echo #
+
+CREATE TABLE t1(a INT, b INT);
+INSERT INTO t1 VALUES (1,2), (3,4), (2,3);
+
+LET $query=
+SELECT *
+FROM
+(
+  SELECT CASE WHEN ((tab2.max_a=1) OR (tab2.max_a=2))
+    THEN 1 ELSE 0 END AS max_a,b
+  FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EVAL $query;
+EVAL EXPLAIN FORMAT=JSON $query;
+
+LET $query=
+SELECT *
+FROM
+(
+  SELECT CASE WHEN ((tab2.max_a=1) OR ((tab2.max_a>2) AND (tab2.max_a<4)))
+    THEN 1 ELSE 0 END AS max_a,b
+  FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EVAL $query;
+EVAL EXPLAIN FORMAT=JSON $query;
+
+LET $query=
+SELECT *
+FROM
+(
+  SELECT CASE WHEN ((tab2.max_a>1) AND ((tab2.max_a=2) OR (tab2.max_a>2)))
+    THEN 1 ELSE 0 END AS max_a,b
+  FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EVAL $query;
+EVAL EXPLAIN FORMAT=JSON $query;
+
+LET $query=
+SELECT *
+FROM
+(
+  SELECT CASE WHEN ((tab2.b=2) OR (tab2.b=4))
+    THEN 1 ELSE 0 END AS max_a,b
+  FROM (SELECT MAX(a) as max_a,b FROM t1 GROUP BY t1.b) AS tab2
+) AS tab1
+WHERE (tab1.max_a=1);
+EVAL $query;
+EVAL EXPLAIN FORMAT=JSON $query;
+
+DROP TABLE t1;

sql/item_cmpfunc.cc

@@ -4970,6 +4970,19 @@ Item *Item_cond::build_clone(THD *thd, MEM_ROOT *mem_root)
 }
 
 
+bool Item_cond::excl_dep_on_grouping_fields(st_select_lex *sel)
+{
+  List_iterator_fast<Item> li(list);
+  Item *item;
+  while ((item= li++))
+  {
+    if (!item->excl_dep_on_grouping_fields(sel))
+      return false;
+  }
+  return true;
+}
+
+
 void Item_cond_and::mark_as_condition_AND_part(TABLE_LIST *embedding)
 {
   List_iterator<Item> li(list);

sql/item_cmpfunc.h

@@ -2224,6 +2224,7 @@ class Item_cond :public Item_bool_func
                 Item_transformer transformer, uchar *arg_t);
   bool eval_not_null_tables(void *opt_arg);
   Item *build_clone(THD *thd, MEM_ROOT *mem_root);
+  bool excl_dep_on_grouping_fields(st_select_lex *sel);
 };
 
 template <template<class> class LI, class T> class Item_equal_iterator;