返回一个空 bitmap, 主要用于 insert 或 stream load 时填充默认值, 如下例:
cat data | curl --location-trusted -u user:passwd -T - \
-H "columns: dt,page,v1,v2=bitmap_empty()" \
http://host:8410/api/test/testDb/_stream_load
BITMAP_EMPTY()
无
返回值的数据类型为 BITMAP
MySQL > select bitmap_count(bitmap_empty());
+------------------------------+
| bitmap_count(bitmap_empty()) |
+------------------------------+
| 0 |
+------------------------------+