[GitHub] [incubator-doris] morningman commented on a change in pull request #4652: [Docs] update data types doc and fix some typo

[GitBox <gi...@apache.org>]

morningman commented on a change in pull request #4652:
URL: https://github.com/apache/incubator-doris/pull/4652#discussion_r499198875



##########
File path: docs/zh-CN/sql-reference/sql-statements/Data Types/BITMAP.md
##########
@@ -0,0 +1,48 @@
+---
+{
+    "title": "BITMAP",
+    "language": "zh-CN"
+}
+---
+
+<!-- 
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License.  You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied.  See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+# BITMAP
+## description
+    BITMAP
+    BITMAP不能作为key列使用，建表时配合聚合类型为BITMAP_UNION。
+    用户不需要指定长度和默认值。长度根据数据的聚合程度系统内控制。
+    并且BITMAP列只能通过配套的bitmap_union_count、bitmap_union、bitmap_hash等函数进行查询或使用。
+    
+    离线场景下使用BITMAP会影响导入速度，在数据量大的情况下查询速度会慢于HLL，并优于Count Distinct。
+    实时场景下BITMAP也不能做到完全的精确去重，通常误差小于千分之一。

Review comment:
       哦，这个描述不太准确。bitmap这个类型本身是精确的。只是在“实时场景”下，用户导入的数据本身是不精确的。比如不使用全局字典，或者使用了 bitmap_hash() 等函数导致的误差，这些和bitmap本身的实现无关。这个需要说明下。




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