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From:timour Date:August 23 2006 1:47pm
Subject:bk commit into 4.1 tree (timour:1.2533) BUG#21456
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Below is the list of changes that have just been committed into a local
4.1 repository of timka. When timka does a push these changes will
be propagated to the main repository and, within 24 hours after the
push, to the public repository.
For information on how to access the public repository
see http://dev.mysql.com/doc/mysql/en/installing-source-tree.html

ChangeSet@stripped, 2006-08-23 16:46:57+03:00, timour@stripped +3 -0
  Bug #21456: SELECT DISTINCT(x) produces incorrect results when using order by
  
  GROUP BY/DISTINCT pruning optimization must be done before ORDER BY 
  optimization because ORDER BY may be removed when GROUP BY/DISTINCT
  sorts as a side effect, e.g. in 
    SELECT DISTINCT <non-key-col>,<pk> FROM t1
    ORDER BY <non-key-col> DISTINCT
  must be removed before ORDER BY as if done the other way around
  it will remove both.

  mysql-test/r/distinct.result@stripped, 2006-08-23 16:46:55+03:00, timour@stripped +11 -0
    Test for BUG#21456.

  mysql-test/t/distinct.test@stripped, 2006-08-23 16:46:55+03:00, timour@stripped +11 -0
    Test for BUG#21456.

  sql/sql_select.cc@stripped, 2006-08-23 16:46:55+03:00, timour@stripped +30 -30
    Bug #21456: SELECT DISTINCT(x) produces incorrect results when using order by
    
    GROUP BY/DISTINCT pruning optimization must be done before ORDER BY 
    optimization because ORDER BY may be removed when GROUP BY/DISTINCT
    sorts as a side effect.

# 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:	timour
# Host:	lamia.home
# Root:	/home/timka/mysql/src/4.1-bug-21456

--- 1.464/sql/sql_select.cc	2006-08-23 16:46:59 +03:00
+++ 1.465/sql/sql_select.cc	2006-08-23 16:46:59 +03:00
@@ -648,6 +648,36 @@ JOIN::optimize()
     if (!order && org_order)
       skip_sort_order= 1;
   }
+  /*
+     Check if we can optimize away GROUP BY/DISTINCT.
+     We can do that if there are no aggregate functions and the
+     fields in DISTINCT clause (if present) and/or columns in GROUP BY
+     (if present) contain direct references to all key parts of
+     an unique index (in whatever order).
+     Note that the unique keys for DISTINCT and GROUP BY should not
+     be the same (as long as they are unique).
+
+     The FROM clause must contain a single non-constant table.
+  */
+  if (tables - const_tables == 1 && (group_list || select_distinct) &&
+      !tmp_table_param.sum_func_count)
+  {
+    if (group_list &&
+       list_contains_unique_index(join_tab[const_tables].table,
+                                 find_field_in_order_list,
+                                 (void *) group_list))
+    {
+      group_list= 0;
+      group= 0;
+    }
+    if (select_distinct &&
+       list_contains_unique_index(join_tab[const_tables].table,
+                                 find_field_in_item_list,
+                                 (void *) &fields_list))
+    {
+      select_distinct= 0;
+    }
+  }
   if (group_list || tmp_table_param.sum_func_count)
   {
     if (! hidden_group_fields && rollup.state == ROLLUP::STATE_NONE)
@@ -716,36 +746,6 @@ JOIN::optimize()
 			     &simple_group);
     if (old_group_list && !group_list)
       select_distinct= 0;
-  }
-  /*
-     Check if we can optimize away GROUP BY/DISTINCT.
-     We can do that if there are no aggregate functions and the
-     fields in DISTINCT clause (if present) and/or columns in GROUP BY
-     (if present) contain direct references to all key parts of
-     an unique index (in whatever order).
-     Note that the unique keys for DISTINCT and GROUP BY should not
-     be the same (as long as they are unique).
-
-     The FROM clause must contain a single non-constant table.
-  */
-  if (tables - const_tables == 1 && (group_list || select_distinct) &&
-      !tmp_table_param.sum_func_count)
-  {
-    if (group_list &&
-       list_contains_unique_index(join_tab[const_tables].table,
-                                 find_field_in_order_list,
-                                 (void *) group_list))
-    {
-      group_list= 0;
-      group= 0;
-    }
-    if (select_distinct &&
-       list_contains_unique_index(join_tab[const_tables].table,
-                                 find_field_in_item_list,
-                                 (void *) &fields_list))
-    {
-      select_distinct= 0;
-    }
   }
   if (!group_list && group)
   {

--- 1.33/mysql-test/r/distinct.result	2006-08-23 16:46:59 +03:00
+++ 1.34/mysql-test/r/distinct.result	2006-08-23 16:46:59 +03:00
@@ -555,3 +555,14 @@ EXPLAIN SELECT DISTINCT a,b,d FROM t2 GR
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t2	ALL	NULL	NULL	NULL	NULL	3	
 DROP TABLE t1,t2;
+CREATE TABLE t1 (a int primary key, b int);
+INSERT INTO t1 (a,b) values (1,1), (2,3), (3,2);
+explain SELECT DISTINCT a, b FROM t1 ORDER BY b;
+id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
+1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	Using filesort
+SELECT DISTINCT a, b FROM t1 ORDER BY b;
+a	b
+1	1
+3	2
+2	3
+DROP TABLE t1;

--- 1.18/mysql-test/t/distinct.test	2006-08-23 16:46:59 +03:00
+++ 1.19/mysql-test/t/distinct.test	2006-08-23 16:46:59 +03:00
@@ -378,4 +378,15 @@ EXPLAIN SELECT DISTINCT a,b,d FROM t2 GR
 
 DROP TABLE t1,t2;
 
+#
+# Bug 21456: SELECT DISTINCT(x) produces incorrect results when using order by
+#
+CREATE TABLE t1 (a int primary key, b int);
+
+INSERT INTO t1 (a,b) values (1,1), (2,3), (3,2);
+
+explain SELECT DISTINCT a, b FROM t1 ORDER BY b;
+SELECT DISTINCT a, b FROM t1 ORDER BY b;
+DROP TABLE t1;
+
 # End of 4.1 tests
Thread
bk commit into 4.1 tree (timour:1.2533) BUG#21456timour23 Aug