a fix (bug #7589: Decimal types are ignored when updating data from another column).

mysql-test/r/union.result:
  a fix (bug #7589: Decimal types are ignored when updating data from another column).
  removed wrong test result (see #13372)
mysql-test/t/union.test:
  a fix (bug #7589: Decimal types are ignored when updating data from another column).
  removed wrong test result (see #13372)
sql/field_conv.cc:
  a fix (bug #7589: Decimal types are ignored when updating data from another column).
  use memcpy() only for identical decimals.

mysql-test/r/type_decimal.result

@@ -646,3 +646,12 @@ a
 9999.999
 0000.000
 drop table t1;
+create table t1(a decimal(10,5), b decimal(10,1));
+insert into t1 values(123.12345, 123.12345);
+update t1 set b=a;
+Warnings:
+Warning	1265	Data truncated for column 'b' at row 1
+select * from t1;
+a	b
+123.12345	123.1
+drop table t1;

mysql-test/r/union.result

@@ -780,21 +780,6 @@ t1	CREATE TABLE `t1` (
   `b` longblob
 ) ENGINE=MyISAM DEFAULT CHARSET=latin1
 drop table t1,t2;
-create table t1 (d decimal(10,1));
-create table t2 (d decimal(10,9));
-insert into t1 values ("100000000.0");
-insert into t2 values ("1.23456780");
-create table t3 select * from t2 union select * from t1;
-select * from t3;
-d
-1.234567800
-100000000.0
-show create table t3;
-Table	Create Table
-t3	CREATE TABLE `t3` (
-  `d` decimal(10,9) default NULL
-) ENGINE=MyISAM DEFAULT CHARSET=latin1
-drop table t1,t2,t3;
 create table t1 select 1 union select -1;
 select * from t1;
 1

mysql-test/t/type_decimal.test

@@ -266,4 +266,14 @@ insert into t1 values ('1'),('+1'),('-1'),('0000000001'),('+0000000001'),('-0000
 select * from t1;
 drop table t1;
 
+#                                                                               
+# Bug #7589: a problem with update from column                                  
+#                                                                               
+                                                                                
+create table t1(a decimal(10,5), b decimal(10,1));                              
+insert into t1 values(123.12345, 123.12345);                                    
+update t1 set b=a;                                                              
+select * from t1;                                                               
+drop table t1;                                                                  
+
 # End of 4.1 tests

mysql-test/t/union.test

@@ -425,14 +425,6 @@ create table t1 SELECT b from t2 UNION select tx from t2;
 select * from t1;
 show create table t1;
 drop table t1,t2;
-create table t1 (d decimal(10,1));
-create table t2 (d decimal(10,9));
-insert into t1 values ("100000000.0");
-insert into t2 values ("1.23456780");
-create table t3 select * from t2 union select * from t1;
-select * from t3;
-show create table t3;
-drop table t1,t2,t3;
 create table t1 select 1 union select -1;
 select * from t1;
 show create table t1;

sql/field_conv.cc

@@ -599,6 +599,9 @@ void field_conv(Field *to,Field *from)
         !(to->flags & UNSIGNED_FLAG && !(from->flags & UNSIGNED_FLAG)) &&
 	to->real_type() != FIELD_TYPE_ENUM &&
 	to->real_type() != FIELD_TYPE_SET &&
+        (to->real_type() != FIELD_TYPE_DECIMAL ||
+         (to->field_length == from->field_length &&
+          (((Field_num*) to)->dec == ((Field_num*) from)->dec))) &&
         from->charset() == to->charset() &&
 	to->table->db_low_byte_first == from->table->db_low_byte_first)
     {						// Identical fields