Fix for BUG#15229.

The cause of this bug was a design flaw due to which the list of natural
join columns was incorrectly computed and stored for nested joins that
are not natural joins, but are operands (possibly indirect) of nested joins.

The patch corrects the flaw in a such a way, that the result columns of a
table reference are materialized only if it is a leaf table (that is, only
if it is a view, stored table, or natural/using join).

1 files changed, 63 insertions, 6 deletions

diff --git a/sql/table.cc b/sql/table.cc
index 268d7a0be49..867ac4fb3bc 100644
--- a/sql/table.cc
+++ b/sql/table.cc
@@ -2816,11 +2816,31 @@ GRANT_INFO *Field_iterator_table_ref::grant()
 
   SYNOPSIS
     Field_iterator_table_ref::get_or_create_column_ref()
-    is_created  [out] set to TRUE if the column was created,
-                      FALSE if we return an already created colum
+    parent_table_ref  the parent table reference over which the
+                      iterator is iterating
 
   DESCRIPTION
-    TODO
+    Create a new natural join column for the current field of the
+    iterator if no such column was created, or return an already
+    created natural join column. The former happens for base tables or
+    views, and the latter for natural/using joins. If a new field is
+    created, then the field is added to 'parent_table_ref' if it is
+    given, or to the original table referene of the field if
+    parent_table_ref == NULL.
+
+  NOTES
+    This method is designed so that when a Field_iterator_table_ref
+    walks through the fields of a table reference, all its fields
+    are created and stored as follows:
+    - If the table reference being iterated is a stored table, view or
+      natural/using join, store all natural join columns in a list
+      attached to that table reference.
+    - If the table reference being iterated is a nested join that is
+      not natural/using join, then do not materialize its result
+      fields. This is OK because for such table references
+      Field_iterator_table_ref iterates over the fields of the nested
+      table references (recursively). In this way we avoid the storage
+      of unnecessay copies of result columns of nested joins.
 
   RETURN
     #     Pointer to a column of a natural join (or its operand)
@@ -2828,22 +2848,28 @@ GRANT_INFO *Field_iterator_table_ref::grant()
 */
 
 Natural_join_column *
-Field_iterator_table_ref::get_or_create_column_ref(bool *is_created)
+Field_iterator_table_ref::get_or_create_column_ref(TABLE_LIST *parent_table_ref)
 {
   Natural_join_column *nj_col;
+  bool is_created= TRUE;
+  uint field_count;
+  TABLE_LIST *add_table_ref= parent_table_ref ?
+                             parent_table_ref : table_ref;
 
-  *is_created= TRUE;
   if (field_it == &table_field_it)
   {
     /* The field belongs to a stored table. */
     Field *field= table_field_it.field();
     nj_col= new Natural_join_column(field, table_ref);
+    field_count= table_ref->table->s->fields;
   }
   else if (field_it == &view_field_it)
   {
     /* The field belongs to a merge view or information schema table. */
     Field_translator *translated_field= view_field_it.field_translator();
     nj_col= new Natural_join_column(translated_field, table_ref);
+    field_count= table_ref->field_translation_end -
+                 table_ref->field_translation;
   }
   else
   {
@@ -2852,12 +2878,43 @@ Field_iterator_table_ref::get_or_create_column_ref(bool *is_created)
       already created via one of the two constructor calls above. In this case
       we just return the already created column reference.
     */
-    *is_created= FALSE;
+    DBUG_ASSERT(table_ref->is_join_columns_complete);
+    is_created= FALSE;
     nj_col= natural_join_it.column_ref();
     DBUG_ASSERT(nj_col);
   }
   DBUG_ASSERT(!nj_col->table_field ||
               nj_col->table_ref->table == nj_col->table_field->table);
+
+  /*
+    If the natural join column was just created add it to the list of
+    natural join columns of either 'parent_table_ref' or to the table
+    reference that directly contains the original field.
+  */
+  if (is_created)
+  {
+    /* Make sure not all columns were materialized. */
+    DBUG_ASSERT(!add_table_ref->is_join_columns_complete);
+    if (!add_table_ref->join_columns)
+    {
+      /* Create a list of natural join columns on demand. */
+      if (!(add_table_ref->join_columns= new List<Natural_join_column>))
+        return NULL;
+      add_table_ref->is_join_columns_complete= FALSE;
+    }
+    add_table_ref->join_columns->push_back(nj_col);
+    /*
+      If new fields are added to their original table reference, mark if
+      all fields were added. We do it here as the caller has no easy way
+      of knowing when to do it.
+      If the fields are being added to parent_table_ref, then the caller
+      must take care to mark when all fields are created/added.
+    */
+    if (!parent_table_ref &&
+        add_table_ref->join_columns->elements == field_count)
+      add_table_ref->is_join_columns_complete= TRUE;
+  }
+
   return nj_col;
 }