bk commit into 4.1 tree (timour:1.2533) BUG#21456

[timour]

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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