bk commit into 4.1 tree (sergefp:1.2102)

[Sergey Petrunia]

Below is the list of changes that have just been committed into a local
4.1 repository of psergey. When psergey does a push these changes will
be propagated to the main repository and, within 24 hours after the
push, to the public repository.
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see http://dev.mysql.com/doc/mysql/en/installing-source-tree.html

ChangeSet
  1.2102 05/03/24 03:20:26 sergefp@stripped +2 -0
  Cleanup in the code that removes checks in conditions  
   * Don't set HA_PART_KEY_SEG for columns that may be NULL, make it 
     mean what its name implies.
   * Added check in test_if_ref, as now HA_PART_KEY_SEG  means what one expects it to.

  sql/table.cc
    1.127 05/03/24 03:20:23 sergefp@stripped +0 -7
    Don't set HA_PART_KEY_SEG for columns that may be NULL, make it mean what 
    is name implies (the corresponding test was adjusted accordingly)

  sql/sql_select.cc
    1.386 05/03/24 03:20:23 sergefp@stripped +28 -3
    Cleanup in the code that removes conditions that are guaranteed to be true from
    the WHERE clause:
     * Made HA_PART_KEY_SEG mean what one expects it to, adjusted the test for it  
       ccordingly
     * Added comments

# This is a BitKeeper patch.  What follows are the unified diffs for the
# set of deltas contained in the patch.  The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User:	sergefp
# Host:	newbox.mylan
# Root:	/home/psergey/mysql-4.1-nulls-scan-t3

--- 1.385/sql/sql_select.cc	2005-03-08 21:45:49 +03:00
+++ 1.386/sql/sql_select.cc	2005-03-24 03:20:23 +03:00
@@ -6798,15 +6798,39 @@
   in sorted order.
 *****************************************************************************/
 
-/* Return 1 if right_item is used removable reference key on left_item */
+/*
+  Check if validity of condition "left_item = right_item" is guaranteed by 
+  use of ref/eq_ref method on left_item's underlying table. If it is, the
+  condition can be removed from the WHERE clause.
+  
+  NOTES
+    The join structures are assumed to have been set accordingly.
+    The criteria is as follows:
+     * condition has form "t1.field1 = t2.field" or "t1.field1 = const_expr"
+     * condition is "same" as one used for ref/eq_ref scan.
+     * condition is NULL-rejecting (as 'ref' guarantees validity of '<=>')
+     * No value truncation/conversion is performed when obtaining key value
+       for ref scan.
+
+  RETURN 
+    1 - The ref/eq_ref access method is used for left_item underlying table 
+        and the condition validity is guaranteed for all rows returned by the
+        access method.
+    0 - Otherwise
+*/
 
 static bool test_if_ref(Item_field *left_item,Item *right_item)
 {
   Field *field=left_item->field;
-  // No need to change const test. We also have to keep tests on LEFT JOIN
+  /*
+    No need to change test if left_item refers to const table.
+    We also have to keep tests on LEFT JOIN 
+    SergeyP: the latter seems to be redundant?
+  */
   if (!field->table->const_table && !field->table->maybe_null)
   {
     Item *ref_item=part_of_refkey(field->table,field);
+    /* value of ref_item will be used as field value in ref/eq_ref access */
     if (ref_item && ref_item->eq(right_item,1))
     {
       if (right_item->type() == Item::FIELD_ITEM)
@@ -6941,7 +6965,8 @@
 
     for (uint part=0 ; part < ref_parts ; part++,key_part++)
       if (field->eq(key_part->field) &&
-	  !(key_part->key_part_flag & HA_PART_KEY_SEG))
+	  !(key_part->key_part_flag & HA_PART_KEY_SEG) &&
+          !key_part->field->real_maybe_null())
 	return table->reginfo.join_tab->ref.items[part];
   }
   return (Item*) 0;

--- 1.126/sql/table.cc	2005-03-04 00:51:18 +03:00
+++ 1.127/sql/table.cc	2005-03-24 03:20:23 +03:00
@@ -664,13 +664,6 @@
 	      field->field_length=key_part->length;
 	    }
 	  }
-	  /*
-	    If the field can be NULL, don't optimize away the test
-	    key_part_column = expression from the WHERE clause
-	    as we need to test for NULL = NULL.
-	  */
-	  if (field->real_maybe_null())
-	    key_part->key_part_flag|= HA_PART_KEY_SEG;
 	}
 	else
 	{					// Error: shorten key