BUG#16393: Let the 'ref' optimizer use ON condition of nested join to construct

'ref' accesses to all tables that are direct children of the nested join and are 
not inner wrt their siblings.


mysql-test/r/join_nested.result:
  Testcase for BUG#16393
mysql-test/t/join_nested.test:
  Testcase for BUG#16393

1 files changed, 68 insertions, 12 deletions

diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index ad6375290cd..9436ad7e840 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -2918,6 +2918,64 @@ sort_keyuse(KEYUSE *a,KEYUSE *b)
 
 
 /*
+  Add to KEY_FIELD array all 'ref' access candidates within nested join
+
+  SYNPOSIS
+    add_key_fields_for_nj()
+      nested_join_table  IN     Nested join pseudo-table to process
+      end                INOUT  End of the key field array
+      and_level          INOUT  And-level
+    
+  DESCRIPTION
+    This function populates KEY_FIELD array with entries generated from the 
+    ON condition of the given nested join, and does the same for nested joins 
+    contained within this nested join.
+    
+  IMPLEMENTATION
+    We can add accesses to the tables that are direct children of this nested 
+    join (1), and are not inner tables w.r.t their neighbours (2).
+    
+    Example for #1 (outer brackets pair denotes nested join this function is 
+    invoked for):
+
+     ... LEFT JOIN (t1 LEFT JOIN (t2 ... ) ) ON cond
+     
+    Example for #2:
+
+     ... LEFT JOIN (t1 LEFT JOIN t2 ) ON cond
+
+    In examples 1-2 for condition cond, we can add 'ref' access candidates to 
+    t1 only.
+    
+    Example #3:
+     
+     ... LEFT JOIN (t1, t2 JOIN t3 ON inner_cond) ON cond
+    
+    Here we can add 'ref' access candidates for t1 and t2, but not for t3.
+    
+*/
+
+static void add_key_fields_for_nj(TABLE_LIST *nested_join_table,
+                                  KEY_FIELD **end, uint *and_level)
+{
+  List_iterator<TABLE_LIST> li(nested_join_table->nested_join->join_list);
+  table_map tables= 0;
+  TABLE_LIST *table;
+  DBUG_ASSERT(nested_join_table->nested_join);
+
+  while ((table= li++))
+  {
+    if (table->nested_join)
+      add_key_fields_for_nj(table, end, and_level);
+    else
+      if (!table->on_expr)
+	tables |= table->table->map;
+  }
+  add_key_fields(end, and_level, nested_join_table->on_expr, tables);
+}
+
+
+/*
   Update keyuse array with all possible keys we can use to fetch rows
   
   SYNOPSIS
@@ -2981,23 +3039,21 @@ update_ref_and_keys(THD *thd, DYNAMIC_ARRAY *keyuse,JOIN_TAB *join_tab,
       into account as well.
     */ 
     if (*join_tab[i].on_expr_ref)
-    {
       add_key_fields(&end,&and_level,*join_tab[i].on_expr_ref,
 		     join_tab[i].table->map);
-    }
-    else 
+  }
+
+  /* Process ON conditions for the nested joins */
+  {
+    List_iterator<TABLE_LIST> li(*join_tab->join->join_list);
+    TABLE_LIST *table;
+    while ((table= li++))
     {
-      TABLE_LIST *tab= join_tab[i].table->pos_in_table_list;
-      TABLE_LIST *embedding= tab->embedding;
-      if (embedding)
-      {
-        NESTED_JOIN *nested_join= embedding->nested_join;
-        if (nested_join->join_list.head() == tab)
-          add_key_fields(&end, &and_level, embedding->on_expr,
-                         nested_join->used_tables);
-      }
+      if (table->nested_join)
+	add_key_fields_for_nj(table, &end, &and_level);
     }
   }
+
   /* fill keyuse with found key parts */
   for ( ; field != end ; field++)
     add_key_part(keyuse,field);