Bug#11766270 59343: YEAR(4): INCORRECT RESULT AND VALGRIND WARNINGS WITH MIN/MAX, UNION

When we create temporary result table for UNION
incorrect max_length for YEAR field is used and
it leads to incorrect field value and incorrect
result string length as YEAR field value calculation
depends on field length.
The fix is to use underlying item max_length for
Item_sum_hybrid::max_length intialization.

mysql-test/r/func_group.result

@@ -1746,4 +1746,15 @@ MAX(LENGTH(a))	LENGTH(MAX(a))	MIN(a)	MAX(a)	CONCAT(MIN(a))	CONCAT(MAX(a))
 20	20	18446668621106209655	18446668621106209655	18446668621106209655	18446668621106209655
 DROP TABLE t1;
 #
+# Bug #11766270  59343: YEAR(4): INCORRECT RESULT AND VALGRIND WARNINGS WITH MIN/MAX, UNION
+#
+CREATE TABLE t1(f1 YEAR(4));
+INSERT INTO t1 VALUES (0000),(2001);
+(SELECT MAX(f1) FROM t1) UNION (SELECT MAX(f1) FROM t1);
+Catalog	Database	Table	Table_alias	Column	Column_alias	Type	Length	Max length	Is_null	Flags	Decimals	Charsetnr
+def				MAX(f1)	MAX(f1)	13	4	4	Y	32864	0	63
+MAX(f1)
+2001
+DROP TABLE t1;
+#
 End of 5.1 tests

mysql-test/t/func_group.test

@@ -1127,6 +1127,18 @@ INSERT INTO t1 VALUES (18446668621106209655);
 SELECT MAX(LENGTH(a)), LENGTH(MAX(a)), MIN(a), MAX(a), CONCAT(MIN(a)), CONCAT(MAX(a)) FROM t1;
 DROP TABLE t1;
 
+--echo #
+--echo # Bug #11766270  59343: YEAR(4): INCORRECT RESULT AND VALGRIND WARNINGS WITH MIN/MAX, UNION
+--echo #
+
+CREATE TABLE t1(f1 YEAR(4));
+INSERT INTO t1 VALUES (0000),(2001);
+--enable_metadata
+(SELECT MAX(f1) FROM t1) UNION (SELECT MAX(f1) FROM t1);
+--disable_metadata
+DROP TABLE t1;
+
+
 --echo #
 --echo End of 5.1 tests
 

sql/field.cc

@@ -5467,6 +5467,7 @@ double Field_year::val_real(void)
 longlong Field_year::val_int(void)
 {
   ASSERT_COLUMN_MARKED_FOR_READ;
+  DBUG_ASSERT(field_length == 2 || field_length == 4);
   int tmp= (int) ptr[0];
   if (field_length != 4)
     tmp%=100;					// Return last 2 char
@@ -5479,6 +5480,7 @@ longlong Field_year::val_int(void)
 String *Field_year::val_str(String *val_buffer,
 			    String *val_ptr __attribute__((unused)))
 {
+  DBUG_ASSERT(field_length < 5);
   val_buffer->alloc(5);
   val_buffer->length(field_length);
   char *to=(char*) val_buffer->ptr();

sql/item_sum.cc

@@ -612,17 +612,13 @@ Item_sum_hybrid::fix_fields(THD *thd, Item **ref)
 
   switch (hybrid_type= item->result_type()) {
   case INT_RESULT:
-    max_length= 20;
-    break;
   case DECIMAL_RESULT:
+  case STRING_RESULT:
     max_length= item->max_length;
     break;
   case REAL_RESULT:
     max_length= float_length(decimals);
     break;
-  case STRING_RESULT:
-    max_length= item->max_length;
-    break;
   case ROW_RESULT:
   default:
     DBUG_ASSERT(0);