bk commit into 5.0 tree (kaa:1.2599) BUG#34512

[Alexey Kopytov]

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5.0 repository of kaa.  When kaa does a push these changes
will be propagated to the main repository and, within 24 hours after the
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see http://dev.mysql.com/doc/mysql/en/installing-source-tree.html

ChangeSet@stripped, 2008-03-06 18:19:47+03:00, kaa@kaamos.(none) +3 -0
  Fix for bug #34512: CAST( AVG( double ) AS DECIMAL )
                      returns wrong results
  
  Casting AVG() to DECIMAL led to incorrect results when the arguments
  had a non-DECIMAL type, because in this case
  Item_sum_avg::val_decimal() performed the division by the number of
  arguments twice.
  
  Fixed by changing Item_sum_avg::val_decimal() to not rely on
  Item_sum_sum::val_decimal(), i.e. calculate sum and divide using
  DECIMAL arithmetics for DECIMAL arguments, and utilize val_real() with
  subsequent conversion to DECIMAL otherwise.

  mysql-test/r/func_group.result@stripped, 2008-03-06 18:19:47+03:00, kaa@kaamos.(none) +6 -0
    Added a test case for bug #34512.

  mysql-test/t/func_group.test@stripped, 2008-03-06 18:19:47+03:00, kaa@kaamos.(none) +10 -0
    Added a test case for bug #34512.

  sql/item_sum.cc@stripped, 2008-03-06 18:19:47+03:00, kaa@kaamos.(none) +9 -1
    Do not use Item_sum_sum::val_decimal() in Item_sum_avg::val_decimal()
    because the first one, depending on the arguments type, may return
    either the sum of the arguments, or the average calculated by the
    virtual val_real() method of Item_sum_avg. Instead, do our own
    calculation based on the arguments type.

diff -Nrup a/mysql-test/r/func_group.result b/mysql-test/r/func_group.result
--- a/mysql-test/r/func_group.result	2008-01-09 17:49:11 +03:00
+++ b/mysql-test/r/func_group.result	2008-03-06 18:19:47 +03:00
@@ -1419,4 +1419,10 @@ Note	1003	select (`test`.`t1`.`a` + 1) A
 DROP VIEW v1;
 DROP TABLE t1;
 SET SQL_MODE=DEFAULT;
+CREATE TABLE t1(a DOUBLE);
+INSERT INTO t1 VALUES (10), (20);
+SELECT AVG(a), CAST(AVG(a) AS DECIMAL) FROM t1;
+AVG(a)	CAST(AVG(a) AS DECIMAL)
+15	15
+DROP TABLE t1;
 End of 5.0 tests
diff -Nrup a/mysql-test/t/func_group.test b/mysql-test/t/func_group.test
--- a/mysql-test/t/func_group.test	2008-01-09 17:49:11 +03:00
+++ b/mysql-test/t/func_group.test	2008-03-06 18:19:47 +03:00
@@ -916,5 +916,15 @@ DROP VIEW v1;
 DROP TABLE t1;
 SET SQL_MODE=DEFAULT;
 
+#
+# Bug #34512: CAST( AVG( double ) AS DECIMAL ) returns wrong results
+#
+
+CREATE TABLE t1(a DOUBLE);
+INSERT INTO t1 VALUES (10), (20);
+SELECT AVG(a), CAST(AVG(a) AS DECIMAL) FROM t1;
+
+DROP TABLE t1;
+
 ###
 --echo End of 5.0 tests
diff -Nrup a/sql/item_sum.cc b/sql/item_sum.cc
--- a/sql/item_sum.cc	2008-02-28 14:31:18 +03:00
+++ b/sql/item_sum.cc	2008-03-06 18:19:47 +03:00
@@ -1206,7 +1206,15 @@ my_decimal *Item_sum_avg::val_decimal(my
     null_value=1;
     return NULL;
   }
-  sum_dec= Item_sum_sum::val_decimal(&sum_buff);
+
+  /*
+    For non-DECIMAL hybrid_type the division will be done in
+    Item_sum_avg::val_real().
+  */
+  if (hybrid_type != DECIMAL_RESULT)
+    return val_decimal_from_real(val);
+
+  sum_dec= dec_buffs + curr_dec_buff;
   int2my_decimal(E_DEC_FATAL_ERROR, count, 0, &cnt);
   my_decimal_div(E_DEC_FATAL_ERROR, val, sum_dec, &cnt, prec_increment);
   return val;