Fix bug #9669 Ordering on IF function with FROM_UNIXTIME function fails

  Integer overflow results in wrong field sortlength.

mysql-test/r/func_if.result

@@ -91,3 +91,20 @@ drop table t1;
 SELECT NULLIF(5,5) IS NULL, NULLIF(5,5) IS NOT NULL;
 NULLIF(5,5) IS NULL	NULLIF(5,5) IS NOT NULL
 1	0
+CREATE TABLE `t1` (
+`id` int(11) NOT NULL ,
+`date` int(10) default NULL,
+`text` varchar(32) NOT NULL
+);
+INSERT INTO t1 VALUES (1,1110000000,'Day 1'),(2,1111000000,'Day 2'),(3,1112000000,'Day 3');
+SELECT id, IF(date IS NULL, '-', FROM_UNIXTIME(date, '%d-%m-%Y')) AS date_ord, text FROM t1 ORDER BY date_ord ASC;
+id	date_ord	text
+1	05-03-2005	Day 1
+2	16-03-2005	Day 2
+3	28-03-2005	Day 3
+SELECT id, IF(date IS NULL, '-', FROM_UNIXTIME(date, '%d-%m-%Y')) AS date_ord, text FROM t1 ORDER BY date_ord DESC;
+id	date_ord	text
+3	28-03-2005	Day 3
+2	16-03-2005	Day 2
+1	05-03-2005	Day 1
+DROP TABLE t1;

mysql-test/t/func_if.test

@@ -61,3 +61,17 @@ drop table t1;
 # Bug #5595  NULLIF() IS NULL returns false if NULLIF() returns NULL
 #
 SELECT NULLIF(5,5) IS NULL, NULLIF(5,5) IS NOT NULL;
+
+#
+# Bug #9669 Ordering on IF function with FROM_UNIXTIME function fails
+#
+CREATE TABLE `t1` (
+  `id` int(11) NOT NULL ,
+  `date` int(10) default NULL,
+  `text` varchar(32) NOT NULL
+);
+INSERT INTO t1 VALUES (1,1110000000,'Day 1'),(2,1111000000,'Day 2'),(3,1112000000,'Day 3');
+SELECT id, IF(date IS NULL, '-', FROM_UNIXTIME(date, '%d-%m-%Y')) AS date_ord, text FROM t1 ORDER BY date_ord ASC;
+SELECT id, IF(date IS NULL, '-', FROM_UNIXTIME(date, '%d-%m-%Y')) AS date_ord, text FROM t1 ORDER BY date_ord DESC;
+DROP TABLE t1;
+

sql/item_cmpfunc.cc

@@ -1227,9 +1227,16 @@ Item_func_if::fix_length_and_dec()
 {
   maybe_null=args[1]->maybe_null || args[2]->maybe_null;
   decimals= max(args[1]->decimals, args[2]->decimals);
-  max_length= (max(args[1]->max_length - args[1]->decimals,
+  if (decimals == NOT_FIXED_DEC)
+  {
+    max_length= max(args[1]->max_length, args[2]->max_length);
+  }
+  else
+  {
+    max_length= (max(args[1]->max_length - args[1]->decimals,
                    args[2]->max_length - args[2]->decimals) +
                decimals);
+  }
   enum Item_result arg1_type=args[1]->result_type();
   enum Item_result arg2_type=args[2]->result_type();
   bool null1=args[1]->const_item() && args[1]->null_value;