Fix bug in handling of decimal fields in UNION statements that could

cause a crash or write to an incorrect memory location. (Bug #14216)

mysql-test/r/union.result

@@ -1253,3 +1253,29 @@ id
 5
 99
 drop table t1;
+create table t1 (f1 decimal(60,25), f2 decimal(60,25));
+insert into t1 values (0.0,0.0);
+select f1 from t1 union all select f2 from t1;
+f1
+0.0000000000000000000000000
+0.0000000000000000000000000
+select 'XXXXXXXXXXXXXXXXXXXX' as description, f1 from t1
+union all
+select 'YYYYYYYYYYYYYYYYYYYY' as description, f2 from t1;
+description	f1
+XXXXXXXXXXXXXXXXXXXX	0.0000000000000000000000000
+YYYYYYYYYYYYYYYYYYYY	0.0000000000000000000000000
+drop table t1;
+create table t1 (f1 decimal(60,24), f2 decimal(60,24));
+insert into t1 values (0.0,0.0);
+select f1 from t1 union all select f2 from t1;
+f1
+0.000000000000000000000000
+0.000000000000000000000000
+select 'XXXXXXXXXXXXXXXXXXXX' as description, f1 from t1
+union all
+select 'YYYYYYYYYYYYYYYYYYYY' as description, f2 from t1;
+description	f1
+XXXXXXXXXXXXXXXXXXXX	0.000000000000000000000000
+YYYYYYYYYYYYYYYYYYYY	0.000000000000000000000000
+drop table t1;

mysql-test/t/union.test

@@ -756,4 +756,22 @@ select 99 union all select id from t1 order by 1;
 select id from t1 union all select 99 order by 1;
 drop table t1;
 
+# 
+# Bug #14216: UNION + DECIMAL wrong values in result
+#
+create table t1 (f1 decimal(60,25), f2 decimal(60,25));
+insert into t1 values (0.0,0.0);
+select f1 from t1 union all select f2 from t1;
+select 'XXXXXXXXXXXXXXXXXXXX' as description, f1 from t1
+union all
+select 'YYYYYYYYYYYYYYYYYYYY' as description, f2 from t1;
+drop table t1;
+create table t1 (f1 decimal(60,24), f2 decimal(60,24));
+insert into t1 values (0.0,0.0);
+select f1 from t1 union all select f2 from t1;
+select 'XXXXXXXXXXXXXXXXXXXX' as description, f1 from t1
+union all
+select 'YYYYYYYYYYYYYYYYYYYY' as description, f2 from t1;
+drop table t1;
+
 # End of 4.1 tests

sql/item.cc

@@ -3274,6 +3274,9 @@ bool Item_type_holder::join_types(THD *thd, Item *item)
     {
       int delta1= max_length_orig - decimals_orig;
       int delta2= item->max_length - item->decimals;
+      if (fld_type == MYSQL_TYPE_DECIMAL)
+        max_length= max(delta1, delta2) + decimals;
+      else
         max_length= min(max(delta1, delta2) + decimals,
                         (fld_type == MYSQL_TYPE_FLOAT) ? FLT_DIG+6 : DBL_DIG+7);
     }