MDEV-15087 Item_func::fix_fields:

           Assertion `used_tables_cache == 0' failed

This bug manifested itself when executing queries
over materialized derived tables /vies and with
conjunctive always true predicates containing
inexpensive single-row subqueries.
This bug disappeared after the patch mdev-15035
had been applied.

mysql-test/r/derived_cond_pushdown.result

@@ -9808,3 +9808,22 @@ EXPLAIN
   }
 }
 DROP TABLE t1;
+#
+# MDEV-15087: error from inexpensive subquery before check
+#                   for condition pushdown into derived 
+#
+CREATE TABLE t1 (i1 int, v1 varchar(1));
+INSERT INTO t1 VALUES (7,'x');
+CREATE TABLE t2 (i1 int);
+INSERT INTO t2 VALUES (8);
+CREATE TABLE t3 (i1 int ,v1 varchar(1), v2 varchar(1));
+INSERT INTO t3 VALUES (4, 'v','v'),(62,'v','k'),(7, 'n', NULL);
+SELECT 1
+FROM (t1 AS a1
+JOIN (((SELECT  DISTINCT t3.*
+FROM t3) AS a2
+JOIN t1 ON (t1.v1 = a2.v2))) ON (t1.v1 = a2.v1))
+WHERE (SELECT  BIT_COUNT(t2.i1)
+FROM (t2 JOIN t3)) IS NULL;
+ERROR 21000: Subquery returns more than 1 row
+DROP TABLE t1, t2, t3;

mysql-test/t/derived_cond_pushdown.test

@@ -1840,3 +1840,28 @@ EVAL $query;
 EVAL EXPLAIN FORMAT=JSON $query;
 
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-15087: error from inexpensive subquery before check
+--echo #                   for condition pushdown into derived 
+--echo #
+
+CREATE TABLE t1 (i1 int, v1 varchar(1));
+INSERT INTO t1 VALUES (7,'x');
+
+CREATE TABLE t2 (i1 int);
+INSERT INTO t2 VALUES (8);
+
+CREATE TABLE t3 (i1 int ,v1 varchar(1), v2 varchar(1));
+INSERT INTO t3 VALUES (4, 'v','v'),(62,'v','k'),(7, 'n', NULL);
+
+--error ER_SUBQUERY_NO_1_ROW
+SELECT 1
+FROM (t1 AS a1
+      JOIN (((SELECT  DISTINCT t3.*
+              FROM t3) AS a2
+             JOIN t1 ON (t1.v1 = a2.v2))) ON (t1.v1 = a2.v1))
+WHERE (SELECT  BIT_COUNT(t2.i1)
+       FROM (t2 JOIN t3)) IS NULL;
+
+DROP TABLE t1, t2, t3;

sql/sql_select.cc

@@ -1368,6 +1368,13 @@ JOIN::optimize_inner()
   conds= optimize_cond(this, conds, join_list, FALSE,
                        &cond_value, &cond_equal, OPT_LINK_EQUAL_FIELDS);
   
+  if (thd->is_error())
+  {
+    error= 1;
+    DBUG_PRINT("error",("Error from optimize_cond"));
+    DBUG_RETURN(1);
+  }
+
   if (thd->lex->sql_command == SQLCOM_SELECT &&
       optimizer_flag(thd, OPTIMIZER_SWITCH_COND_PUSHDOWN_FOR_DERIVED))
   {
@@ -1402,13 +1409,6 @@ JOIN::optimize_inner()
       DBUG_RETURN(1);
   }
      
-  if (thd->is_error())
-  {
-    error= 1;
-    DBUG_PRINT("error",("Error from optimize_cond"));
-    DBUG_RETURN(1);
-  }
-
   {
     having= optimize_cond(this, having, join_list, TRUE,
                           &having_value, &having_equal);