bk commit into 4.1 tree (gkodinov:1.2583) BUG#15881

[kgeorge]

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ChangeSet@stripped, 2006-12-13 14:34:19+02:00, gkodinov@stripped +3 -0
  Bug #15881: cast problems
   The optimizer removes expressions from GROUP BY/DISTINCT
   if they happen to participate in a <expression> = <const>
   predicates of the WHERE clause (the idea being that if
   it's always equal to a constant it can't have multiple 
   values).
   However for predicates where the expression and the 
   constant item are of different result type this is not
   valid (e.g. a string column compared to 0).
   Fixed by disabling the usage of predicates that compare 
   expressions and constants of different result type when 
   simplifying GROUP BY/DISTINCT.

  mysql-test/r/distinct.result@stripped, 2006-12-13 14:34:12+02:00, gkodinov@stripped +11
-0
    Bug #15881: cast problems
     - test case

  mysql-test/t/distinct.test@stripped, 2006-12-13 14:34:13+02:00, gkodinov@stripped +8 -0
    Bug #15881: cast problems
     - test case

  sql/sql_select.cc@stripped, 2006-12-13 14:34:14+02:00, gkodinov@stripped +32 -2
    Bug #15881: cast problems
     - can't use <expr>=<const> to remove GROUP BY/DISTINCT cols
       if they're not of the same type.

# 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:	gkodinov
# Host:	macbook.gmz
# Root:	/Users/kgeorge/mysql/work/B15881-4.1-opt

--- 1.465/sql/sql_select.cc	2006-11-03 00:20:32 +02:00
+++ 1.466/sql/sql_select.cc	2006-12-13 14:34:14 +02:00
@@ -4896,6 +4896,36 @@ remove_eq_conds(THD *thd, COND *cond, It
   return cond;					// Point at next and level
 }
 
+/* 
+  Check if comparison args can be used for removal of GROUP BY/DISTINCT
+  
+  SYNOPSIS
+    is_permutable_const_expression_args()
+      l          the left comparison argument
+      l          the right comparison argument
+  
+  DESCRIPTION    
+    Checks if the args of equal comparioson can be used to take 
+    away DISTINCT/GROUP BY : generally <expr> == <const>.
+    Arguments must be of the same type because e.g. 
+    <string_field> = <int_const> may match more than 1 row. 
+    We must take into coinsideration and the optimization done for various 
+    string constants when compared to dates etc (see Item_int_with_ref)
+  
+  RETURN VALUE  
+    TRUE    can be used
+    FALSE   cannot be used
+*/
+static bool
+is_permutable_const_expression_args(Item *l, Item *r)
+{
+  return r->const_item() &&
+    (r->result_type() == l->result_type() ||
+     (l->type() == Item::FIELD_ITEM && 
+      ((Item_field *)l)->field->can_be_compared_as_longlong() &&
+      r->result_type() == INT_RESULT));
+}
+
 /*
   Return 1 if the item is a const value in all the WHERE clause
 */
@@ -4932,7 +4962,7 @@ const_expression_in_where(COND *cond, It
     Item *right_item= ((Item_func*) cond)->arguments()[1];
     if (left_item->eq(comp_item,1))
     {
-      if (right_item->const_item())
+      if (is_permutable_const_expression_args (left_item, right_item))
       {
 	if (*const_item)
 	  return right_item->eq(*const_item, 1);
@@ -4942,7 +4972,7 @@ const_expression_in_where(COND *cond, It
     }
     else if (right_item->eq(comp_item,1))
     {
-      if (left_item->const_item())
+      if (is_permutable_const_expression_args (right_item, left_item))
       {
 	if (*const_item)
 	  return left_item->eq(*const_item, 1);

--- 1.35/mysql-test/r/distinct.result	2006-11-29 00:21:37 +02:00
+++ 1.36/mysql-test/r/distinct.result	2006-12-13 14:34:12 +02:00
@@ -625,3 +625,14 @@ fruit_id	fruit_name
 2	APPLE
 DROP TABLE t1;
 DROP TABLE t2;
+CREATE TABLE t1 (a CHAR(1));
+INSERT INTO t1 VALUES('A'), (0);
+SELECT a FROM t1 WHERE a=0;
+a
+A
+0
+SELECT DISTINCT a FROM t1 WHERE a=0;
+a
+A
+0
+DROP TABLE t1;

--- 1.20/mysql-test/t/distinct.test	2006-11-29 00:21:37 +02:00
+++ 1.21/mysql-test/t/distinct.test	2006-12-13 14:34:13 +02:00
@@ -454,4 +454,12 @@ SELECT * FROM t2;
 DROP TABLE t1;
 DROP TABLE t2;
 
+#
+# Bug #15881: cast problems
+#
+CREATE TABLE t1 (a CHAR(1)); INSERT INTO t1 VALUES('A'), (0);
+SELECT a FROM t1 WHERE a=0;
+SELECT DISTINCT a FROM t1 WHERE a=0;
+DROP TABLE t1;
+
 # End of 4.1 tests