[fix](decimal) fix cast rounding half up with negative number (#22450)

be/src/vec/data_types/data_type_decimal.h

@@ -505,7 +505,11 @@ void convert_decimal_cols(
         MaxNativeType multiplier =
                 DataTypeDecimal<MaxFieldType>::get_scale_multiplier(scale_from - scale_to);
         for (size_t i = 0; i < sz; i++) {
-            vec_to[i] = (vec_from[i] + multiplier / 2) / multiplier;
+            if (vec_from[i] >= 0) {
+                vec_to[i] = (vec_from[i] + multiplier / 2) / multiplier;
+            } else {
+                vec_to[i] = (vec_from[i] - multiplier / 2) / multiplier;
+            }
         }
     }
 

regression-test/data/correctness/test_cast_as_decimalv3.out

@@ -12,3 +12,15 @@
 0.25000
 0.20000
 
+-- !select4 --
+-280.0000
+
+-- !select5 --
+-280.0001
+
+-- !select6 --
+-280.0000
+
+-- !select7 --
+-280.0001
+

regression-test/suites/correctness/test_cast_as_decimalv3.groovy

@@ -30,7 +30,7 @@ suite("test_cast_as_decimalv3") {
         );
     """
     sql """
-        set enable_nereids_planner=false,enable_fold_constant_by_be = false
+        set enable_nereids_planner=true,enable_fold_constant_by_be = false
     """
     sql """
         INSERT INTO divtest VALUES(1,3.00)
@@ -50,4 +50,22 @@ suite("test_cast_as_decimalv3") {
     qt_select3 """
         select 1.0 / val from divtest order by id
     """
+    qt_select4 """
+        select cast(-280.00000000 as decimal(16,4));
+    """
+    qt_select5 """
+        select cast(-280.00005000 as decimal(16,4));
+    """
+
+    sql """
+        set enable_nereids_planner=false
+    """
+
+
+    qt_select6 """
+        select cast(-280.00000000 as decimal(16,4));
+    """
+    qt_select7 """
+        select cast(-280.00005000 as decimal(16,4));
+    """
 }