Fix for bug #13372 (decimal union)

mysql-test/r/type_decimal.result

-DROP TABLE IF EXISTS t1;
+DROP TABLE IF EXISTS t1, t2, t3;
 SET SQL_WARNINGS=1;
 CREATE TABLE t1 (
 id int(11) NOT NULL auto_increment,
@@ -655,3 +655,18 @@ select * from t1;
 a	b
 123.12345	123.1
 drop table t1;
+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
+100000000.000000000
+show create table t3;
+Table	Create Table
+t3	CREATE TABLE `t3` (
+  `d` decimal(18,9) default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1, t2, t3;

mysql-test/r/type_float.result

@@ -235,3 +235,18 @@ select * from t1 where reckey=1.09E2;
 reckey	recdesc
 109	Has 109 as key
 drop table t1;
+create table t1 (d double(10,1));
+create table t2 (d double(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
+100000000.000000000
+show create table t3;
+Table	Create Table
+t3	CREATE TABLE `t3` (
+  `d` double(61,9) default NULL
+) ENGINE=MyISAM DEFAULT CHARSET=latin1
+drop table t1, t2, t3;

mysql-test/t/type_decimal.test

 # bug in decimal() with negative numbers by kaido@tradenet.ee
 
 --disable_warnings
-DROP TABLE IF EXISTS t1;
+DROP TABLE IF EXISTS t1, t2, t3;
 --enable_warnings
 SET SQL_WARNINGS=1;
 
@@ -276,4 +276,16 @@ update t1 set b=a;
 select * from t1;                                                               
 drop table t1;                                                                  
 
+#
+# Bug #13372 (decimal union)
+#
+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;
+
 # End of 4.1 tests

mysql-test/t/type_float.test

@@ -149,4 +149,17 @@ select * from t1 where reckey=109;
 select * from t1 where reckey=1.09E2;
 drop table t1;
 
+#
+# Bug #13372 (decimal union)
+#
+create table t1 (d double(10,1));
+create table t2 (d double(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;
+
+
 # End of 4.1 tests

sql/item.cc

@@ -3205,9 +3205,14 @@ enum_field_types Item_type_holder::get_real_type(Item *item)
 
 bool Item_type_holder::join_types(THD *thd, Item *item)
 {
+  uint max_length_orig= max_length;
+  uint decimals_orig= decimals;
   max_length= max(max_length, display_length(item));
+  decimals= max(decimals, item->decimals);
   fld_type= Field::field_type_merge(fld_type, get_real_type(item));
-  if (Field::result_merge_type(fld_type) == STRING_RESULT)
+  switch (Field::result_merge_type(fld_type))
+  {
+  case STRING_RESULT:
   {
     const char *old_cs, *old_derivation;
     old_cs= collation.collation->name;
@@ -3221,8 +3226,23 @@ bool Item_type_holder::join_types(THD *thd, Item *item)
 	       "UNION");
       return TRUE;
     }
+    break;
   }
+  case REAL_RESULT:
+  {
     decimals= max(decimals, item->decimals);
+    if (decimals != NOT_FIXED_DEC)
+    {
+      int delta1= max_length_orig - decimals_orig;
+      int delta2= item->max_length - item->decimals;
+      max_length= max(delta1, delta2) + decimals;
+    }
+    else
+      max_length= (fld_type == MYSQL_TYPE_FLOAT) ? FLT_DIG+6 : DBL_DIG+7;
+    break;
+  }
+  default:;
+  };
   maybe_null|= item->maybe_null;
   get_full_info(item);
   return FALSE;