MDEV-7691: Assertion `outer_context || !*from_field || *from_field == not_found_field' ...

The bug occurred when a subquery
- has a reference to outside, to grand-parent query or further up
- is converted to a semi-join (i.e. merged into its parent).

Then the reference to outside had form Item_ref(Item_field(...)).
- Conversion to semi-join would call item->fix_after_pullout() for the
  outside reference.
- Item_ref::fix_after_pullout would call Item_field->fix_after_pullout
- The Item_field would construct a new Name_resolution_context object
  This process ignored the fact that the Item_field does not belong to
  any of the subselects being flattened.
The result was crash in the next call to Item_field::fix_fields(), where
we would try to use an invalid Name_resolution_context object.

Fixed by not creating Name_resolution_context object if the Item_field's
context does not belong to the subselect(s) that were flattened.

1 files changed, 39 insertions, 0 deletions

diff --git a/mysql-test/r/subselect4.result b/mysql-test/r/subselect4.result
index c7f22cf05e5..89fb0902f53 100644
--- a/mysql-test/r/subselect4.result
+++ b/mysql-test/r/subselect4.result
@@ -2410,5 +2410,44 @@ SELECT x FROM t1 WHERE id > (SELECT MAX(id) - 1000 FROM t1) ORDER BY x LIMIT 1;
 x
 0
 drop table t1;
+#
+# MDEV-7691: Assertion `outer_context || !*from_field || *from_field == not_found_field' ...
+#
+set optimizer_switch=default;
+CREATE TABLE t1 (a INT) ENGINE=MyISAM;
+INSERT INTO t1 VALUES (4),(6);
+CREATE TABLE t2 (b INT) ENGINE=MyISAM;
+INSERT INTO t2 VALUES (1),(8);
+PREPARE stmt FROM "
+SELECT * FROM t2
+HAVING 0 IN (
+  SELECT a FROM t1
+  WHERE a IN ( 
+    SELECT a FROM t1
+    WHERE b = a
+  )
+)
+";
+EXECUTE stmt;
+b
+EXECUTE stmt;
+b
+# Alternative test case, without HAVING
+CREATE TABLE t3 (i INT) ENGINE=MyISAM;
+INSERT INTO t3 VALUES (4),(6);
+PREPARE stmt FROM "
+SELECT * FROM t3 AS t10
+WHERE EXISTS ( 
+  SELECT * FROM t3 AS t20 WHERE t10.i IN ( 
+    SELECT i FROM t3 
+  ) 
+)";
+EXECUTE stmt;
+i
+6
+EXECUTE stmt;
+i
+6
+drop table t1, t2, t3;
 SET optimizer_switch= @@global.optimizer_switch;
 set @@tmp_table_size= @@global.tmp_table_size;