Fix bitmap internal _type misuse

be/src/util/bitmap_value.h

@@ -993,6 +993,10 @@ class BitmapValue {
                 _type = SINGLE;
                 break;
             case SINGLE:
+                //there is no need to convert the type if two variables are equal
+                if (_sv == value) {
+                    break;
+                }
                 _bitmap.add(_sv);
                 _bitmap.add(value);
                 _type = BITMAP;

be/test/util/bitmap_value_test.cpp

@@ -14,14 +14,14 @@
 // KIND, either express or implied.  See the License for the
 // specific language governing permissions and limitations
 // under the License.
-#include "util/bitmap_value.h"
 
 #include <cstdint>
 #include <gtest/gtest.h>
 #include <string>
-#include <vector>
 
 #include "util/coding.h"
+#define private public
+#include "util/bitmap_value.h"
 
 namespace doris {
 
@@ -304,9 +304,30 @@ TEST(BitmapValueTest, bitmap_to_string) {
     empty.add(2);
     ASSERT_STREQ("1,2", empty.to_string().c_str());
 }
+
+TEST(BitmapValueTest, bitmap_single_convert) {
+    BitmapValue bitmap;
+    ASSERT_STREQ("", bitmap.to_string().c_str());
+    bitmap.add(1);
+    ASSERT_STREQ("1", bitmap.to_string().c_str());
+    bitmap.add(1);
+    ASSERT_STREQ("1", bitmap.to_string().c_str());
+    ASSERT_EQ(BitmapValue::SINGLE, bitmap._type);
+
+    BitmapValue bitmap_u;
+    bitmap_u.add(1);
+    bitmap |= bitmap_u;
+    ASSERT_EQ(BitmapValue::SINGLE, bitmap._type);
+
+    bitmap_u.add(2);
+    ASSERT_EQ(BitmapValue::BITMAP, bitmap_u._type);
+
+    bitmap |= bitmap_u;
+    ASSERT_EQ(BitmapValue::BITMAP, bitmap._type);
+}
 } // namespace doris
 
 int main(int argc, char** argv) {
     ::testing::InitGoogleTest(&argc, argv);
     return RUN_ALL_TESTS();
-}
+}