MDEV-15777 Use inferred IS NOT NULL predicates in the range optimizer

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 913442ee22d..af908d9d553 100644
--- a/sql/item_func.cc
+++ b/sql/item_func.cc
@@ -404,6 +404,25 @@ 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)
 {