MDEV-21265: IN predicate conversion to IN subquery should be allowed for a broader set of datatype comparisonbb-10.3-21265

Allow materialization strategy when collations on the
inner and outer sides of an IN subquery are the same and the
character set of the inner side is a proper subset of the character
set on the outer side.
This allows conversion from utf8mb3 to utf8mb4
as the former is a subset of the later.
This is only allowed when IN predicate is converted to an IN subquery

Backported part of the patch (d6a00d9b18f) of MDEV-17905.

1 files changed, 4 insertions, 2 deletions

diff --git a/sql/sql_tvc.cc b/sql/sql_tvc.cc
index def519035d9..10a279b92ed 100644
--- a/sql/sql_tvc.cc
+++ b/sql/sql_tvc.cc
@@ -829,7 +829,8 @@ static bool cmp_row_types(Item* item1, Item* item2)
     Item *inner= item1->element_index(i);
     Item *outer= item2->element_index(i);
     if (!inner->type_handler()->subquery_type_allows_materialization(inner,
-                                                                     outer))
+                                                                     outer,
+                                                                     true))
       return true;
   }
   return false;
@@ -895,7 +896,7 @@ Item *Item_func_in::in_predicate_to_in_subs_transformer(THD *thd,
   
   for (uint i=1; i < arg_count; i++)
   {
-    if (!args[i]->const_item() || cmp_row_types(args[0], args[i]))
+    if (!args[i]->const_item() || cmp_row_types(args[i], args[0]))
       return this;
   }
 
@@ -975,6 +976,7 @@ Item *Item_func_in::in_predicate_to_in_subs_transformer(THD *thd,
   if (!(in_subs=
           new (thd->mem_root) Item_in_subselect(thd, args[0], sq_select)))
     goto err;
+  in_subs->converted_from_in_predicate= TRUE;
   sq= in_subs;
   if (negated)
     sq= negate_expression(thd, in_subs);