MDEV-10776: Server crash on query

Exclude untouched in prepare phese subqueries from the select/unit tree
because they became unreachable by execution.

1 files changed, 18 insertions, 2 deletions

diff --git a/sql/sql_lex.cc b/sql/sql_lex.cc
index 2462f0fea17..f2e7b4f7c3a 100644
--- a/sql/sql_lex.cc
+++ b/sql/sql_lex.cc
@@ -3486,12 +3486,28 @@ bool st_select_lex::add_index_hint (THD *thd, char *str, uint length)
 
 bool st_select_lex::optimize_unflattened_subqueries(bool const_only)
 {
-  for (SELECT_LEX_UNIT *un= first_inner_unit(); un; un= un->next_unit())
+  SELECT_LEX_UNIT *next_unit= NULL;
+  for (SELECT_LEX_UNIT *un= first_inner_unit();
+       un;
+       un= next_unit ? next_unit : un->next_unit())
   {
     Item_subselect *subquery_predicate= un->item;
-    
+    next_unit= NULL;
+
     if (subquery_predicate)
     {
+      if (!subquery_predicate->fixed)
+      {
+	/*
+	 This subquery was excluded as part of some expression so it is
+	 invisible from all prepared expression.
+       */
+	next_unit= un->next_unit();
+	un->exclude_level();
+	if (next_unit)
+	  continue;
+	break;
+      }
       if (subquery_predicate->substype() == Item_subselect::IN_SUBS)
       {
         Item_in_subselect *in_subs= (Item_in_subselect*) subquery_predicate;