MDEV-15777 Use inferred IS NOT NULL predicates in the range optimizer10.3-mdev15777

This patch introduces the optimization that allows range optimizer to
consider index range scans that are built employing NOT NULL predicates
inferred from WHERE conditions and ON expressions.
The patch adds a new optimizer switch not_null_range_scan.

1 files changed, 19 insertions, 0 deletions

diff --git a/sql/item_func.cc b/sql/item_func.cc
index a030d2f8681..41bbd2ea8f0 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -403,6 +403,25 @@ Item_func::eval_not_null_tables(void *opt_arg)
 }
 
 
+bool
+Item_func::find_not_null_fields(table_map allowed)
+{
+  if (~allowed & used_tables())
+    return false;
+
+  Item **arg,**arg_end;
+  if (arg_count)
+  {
+    for (arg=args, arg_end=args+arg_count; arg != arg_end ; arg++)
+    {
+      if (!(*arg)->find_not_null_fields(allowed))
+        continue;
+    }
+  }
+  return false;
+}
+
+
 void Item_func::fix_after_pullout(st_select_lex *new_parent, Item **ref,
                                   bool merge)
 {