MDEV-19834 Selectivity of an equality condition discounted twice

When discounting selectivity of ref access, don't discount the
selectivity we've already discounted for range access.

The 10.1 version of the fix. Will need to adjust condition filtering
test results in 10.4

1 files changed, 9 insertions, 6 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index fb8e4755b1d..29fc3f80ed0 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -7618,6 +7618,7 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
     KEYUSE *keyuse= pos->key;
     KEYUSE *prev_ref_keyuse= keyuse;
     uint key= keyuse->key;
+    bool used_range_selectivity= false;
     
     /*
       Check if we have a prefix of key=const that matches a quick select.
@@ -7643,6 +7644,7 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
           keyparts++;
         }
         sel /= (double)table->quick_rows[key] / (double) table->stat_records();
+        used_range_selectivity= true;
       }
     }
     
@@ -7678,13 +7680,14 @@ double table_cond_selectivity(JOIN *join, uint idx, JOIN_TAB *s,
           if (keyparts > keyuse->keypart)
 	  {
             /* Ok this is the keyuse that will be used for ref access */
-            uint fldno;
-            if (is_hash_join_key_no(key))
-	      fldno= keyuse->keypart;
-            else
-              fldno= table->key_info[key].key_part[keyparts-1].fieldnr - 1;
-            if (keyuse->val->const_item())
+            if (!used_range_selectivity && keyuse->val->const_item())
             { 
+              uint fldno;
+              if (is_hash_join_key_no(key))
+                fldno= keyuse->keypart;
+              else
+                fldno= table->key_info[key].key_part[keyparts-1].fieldnr - 1;
+
               if (table->field[fldno]->cond_selectivity > 0)
 	      {            
                 sel /= table->field[fldno]->cond_selectivity;