morningman commented on a change in pull request #3584:
URL: https://github.com/apache/incubator-doris/pull/3584#discussion_r428443827
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File path: docs/zh-CN/administrator-guide/outfile.md
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+---
+{
+ "title": "导出查询结果集",
+ "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.
+-->
+
+# 导出查询结果集
+
+本文档介绍如何使用 `SELECT INTO OUTFILE` 命令进行查询结果的导入操作。
+
+## 语法
+
+`SELECT INTO OUTFILE` 语句可以将查询结果导出到文件中。目前仅支持通过 Broker 进程导出到远端存储，如 HDFS，S3，BOS
上。语法如下
+
+```
+query_stmt
+INTO OUTFILE "file_path"
+[format_as]
+WITH BROKER `broker_name`
+[broker_properties]
+[other_properties]
+```
+
+* `file_path`
+
+ `file_path` 指向文件存储的路径以及文件前缀。如 `hdfs://path/to/my_file`。
+
+ 最终的文件名将由 `my_file`，文件序号以及文件格式后缀组成。其中文件序号由0开始，数量为文件被分割的数量。如：
+
+ ```
+ my_file_0.csv
+ my_file_1.csv
+ my_file_2.csv
+ ```
+
+* `[format_as]`
+
+ ```
+ FORMAT AS CSV
+ ```
+
+ 指定导出格式。默认为 CSV。
+
+* `[broker_properties]`
+
+ ```
+ ("broker_prop_key" = "broker_prop_val", ...)
+ ```
+
+ Broker 相关的一些参数，如 HDFS 的 认证信息等。具体参阅[Broker 文档](./broker.html)。
+
+* `[other_properties]`
+
+ ```
+ ("key1" = "val1", "key2" = "val2", ...)
+ ```
+
+ 其他属性，目前支持以下属性：
+
+ * `column_separator`：列分隔符，仅对 CSV 格式适用。默认为 `\t`。
+ * `line_delimiter`：行分隔符，仅对 CSV 格式适用。默认为 `\n`。
+ * `max_file_size_bytes`：单个文件的最大大小。默认为 1GB。取值范围在 5MB 到 2GB
之间。超过这个大小的文件将会被切分。
+
+1. 示例1
+
+ 将简单查询结果导出到文件 `hdfs:/path/to/result.txt`。指定导出格式为 CSV。使用 `my_broker` 并设置
kerberos 认证信息。指定列分隔符为 `,`，行分隔符为 `\n`。
+
+ ```
+ SELECT * FROM tbl
+ INTO OUTFILE "hdfs:/path/to/result"
+ FORMAT AS CSV
+ WITH BROKER "my_broker"
+ (
+ "hadoop.security.authentication" = "kerberos",
+ "kerberos_principal" = "do...@your.com",
+ "kerberos_keytab" = "/home/doris/my.keytab"
+ )
+ PROPERTIELS
+ (
+ "column_separator" = ",",
+ "line_delimiter" = "\n",
+ "max_file_size_bytes" = "100MB"
+ );
+ ```
+
+ 最终生成文件如如果不大于 100MB，则为：`result_0.csv`。
+
+ 如果大于 100MB，则可能为 `result_0.csv, result_1.csv, ...`。
+
+2. 示例2
+
+ 将 CTE 语句的查询结果导出到文件 `hdfs:/path/to/result.txt`。默认导出格式为 CSV。使用 `my_broker`
并设置 hdfs 高可用信息。使用默认的行列分隔符。
+
+ ```
+ WITH
+ x1 AS
+ (SELECT k1, k2 FROM tbl1),
+ x2 AS
+ (SELECT k3 FROM tbl2)
+ SELEC k1 FROM x1 UNION SELECT k3 FROM x2
+ INTO OUTFILE "hdfs:/path/to/result.txt"
+ WITH BROKER "my_broker"
+ (
+ "username"="user",
+ "password"="passwd",
+ "dfs.nameservices" = "my_ha",
+ "dfs.ha.namenodes.my_ha" = "my_namenode1, my_namenode2",
+ "dfs.namenode.rpc-address.my_ha.my_namenode1" = "nn1_host:rpc_port",
+ "dfs.namenode.rpc-address.my_ha.my_namenode2" = "nn2_host:rpc_port",
+ "dfs.client.failover.proxy.provider" =
"org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider"
+ );
+ ```
+
+ 最终生成文件如如果不大于 1GB，则为：`result_0.csv`。
+
+ 如果大于 1GB，则可能为 `result_0.csv, result_1.csv, ...`。
+
+3. 示例3
+
+ 将 UNION 语句的查询结果导出到文件 `bos://bucket/result.txt`。指定导出格式为 PARQUET。使用
`my_broker` 并设置 hdfs 高可用信息。PARQUET 格式无需指定列分割符。
+
+ ```
+ SELECT k1 FROM tbl1 UNION SELECT k2 FROM tbl1
+ INTO OUTFILE "bos://bucket/result.txt"
+ FORMAT AS PARQUET
+ WITH BROKER "my_broker"
+ (
+ "bos_endpoint" = "http://bj.bcebos.com";,
+ "bos_accesskey" = "xxxxxxxxxxxxxxxxxxxxxxxxxx",
+ "bos_secret_accesskey" = "yyyyyyyyyyyyyyyyyyyyyyyyyy"
+ )
+ ```
+
+ 最终生成文件如如果不大于 1GB，则为：`result_0.parquet`。
+
+ 如果大于 1GB，则可能为 `result_0.parquet, result_1.parquet, ...`。
+
+## 返回结果
+
+导出命令为同步命令。命令返回，即表示操作结束。
+
+如果正常导出并返回，则结果如下：
+
+```
+mysql> SELECT * FROM tbl INTO OUTFILE ...
Query OK, 100000 row
affected (5.86 sec)
+```
+
+其中 `100000 row affected` 表示导出的结果集行数。
+
+如果执行错误，则会返回错误信息，如：
+
+```
+mysql> SELECT * FROM tbl INTO OUTFILE ...
ERROR 1064 (HY000):
errCode = 2, detailMessage = Open broker writer failed ...
+```
+
+## 注意事项
+
+* 查询结果是由单个 BE 节点，单线程导出的。因此导出时间和导出结果集大小正相关。
Review comment:
这里目前只是简单复用了查询返回结果的逻辑。
多线程的支持会麻烦一点。比如需要判断select语句是否包含order by 等信息。如果包含，则只能使用单线程顺序写（因为结果是顺序返回的）。
即使不包含order
by，目前查询框架结果还是单线程返回的，最多是改成多线程写文件。但是很多远端系统不支持指定offset写，所以多个线程只能写到多个文件里。也比较麻烦。
不太确定其他系统对于select结果的导出具体是怎么实现的。
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