druid-docs-cn/Tutorials/chapter-4.md

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## 查询数据
本教程将以Druid SQL和Druid的原生查询格式的示例演示如何在Apache Druid中查询数据。
本教程假定您已经完成了摄取教程之一因为我们将查询Wikipedia编辑样例数据。
* [加载本地文件](./chapter-1.md)
* [从Kafka加载数据](./chapter-2.md)
* [从Hadoop加载数据](./chapter-3.md)
Druid查询通过HTTP发送,Druid控制台包括一个视图用于向Druid发出查询并很好地格式化结果。
### Druid SQL查询
Druid支持SQL查询。
该查询检索了2015年9月12日被编辑最多的10个维基百科页面
```
SELECT page, COUNT(*) AS Edits
FROM wikipedia
WHERE TIMESTAMP '2015-09-12 00:00:00' <= "__time" AND "__time" < TIMESTAMP '2015-09-13 00:00:00'
GROUP BY page
ORDER BY Edits DESC
LIMIT 10
```
让我们来看几种不同的查询方法
#### 通过控制台查询SQL
您可以通过在控制台中进行上述查询:
![](img-3/tutorial-query-01.png)
控制台查询视图通过内联文档提供自动补全功能。
![](img-3/tutorial-query-02.png)
您还可以从 `...` 选项菜单中配置要与查询一起发送的其他上下文标志。
请注意控制台将默认情况下使用带Limit的SQL查询以便可以完成诸如`SELECT * FROM wikipedia`之类的查询,您可以通过 `Smart query limit` 切换关闭此行为。
![](img-3/tutorial-query-03.png)
查询视图提供了可以为您编写和修改查询的上下文操作。
#### 通过dsql查询SQL
为方便起见Druid软件包中包括了一个SQL命令行客户端位于Druid根目录中的 `bin/dsql`
运行 `bin/dsql`, 可以看到如下:
```
Welcome to dsql, the command-line client for Druid SQL.
Type "\h" for help.
dsql>
```
将SQl粘贴到 `dsql` 中提交查询:
```
dsql> SELECT page, COUNT(*) AS Edits FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00' GROUP BY page ORDER BY Edits DESC LIMIT 10;
┌──────────────────────────────────────────────────────────┬───────┐
│ page │ Edits │
├──────────────────────────────────────────────────────────┼───────┤
│ Wikipedia:Vandalismusmeldung │ 33 │
│ User:Cyde/List of candidates for speedy deletion/Subpage │ 28 │
│ Jeremy Corbyn │ 27 │
│ Wikipedia:Administrators' noticeboard/Incidents │ 21 │
│ Flavia Pennetta │ 20 │
│ Total Drama Presents: The Ridonculous Race │ 18 │
│ User talk:Dudeperson176123 │ 18 │
│ Wikipédia:Le Bistro/12 septembre 2015 │ 18 │
│ Wikipedia:In the news/Candidates │ 17 │
│ Wikipedia:Requests for page protection │ 17 │
└──────────────────────────────────────────────────────────┴───────┘
Retrieved 10 rows in 0.06s.
```
#### 通过HTTP查询SQL
SQL查询作为JSON通过HTTP提交
教程包括一个示例文件, 该文件`quickstart/tutorial/wikipedia-top-pages-sql.json`包含上面显示的SQL查询, 我们将该查询提交给Druid Broker。
```
curl -X 'POST' -H 'Content-Type:application/json' -d @quickstart/tutorial/wikipedia-top-pages-sql.json http://localhost:8888/druid/v2/sql
```
结果返回如下:
```
[
{
"page": "Wikipedia:Vandalismusmeldung",
"Edits": 33
},
{
"page": "User:Cyde/List of candidates for speedy deletion/Subpage",
"Edits": 28
},
{
"page": "Jeremy Corbyn",
"Edits": 27
},
{
"page": "Wikipedia:Administrators' noticeboard/Incidents",
"Edits": 21
},
{
"page": "Flavia Pennetta",
"Edits": 20
},
{
"page": "Total Drama Presents: The Ridonculous Race",
"Edits": 18
},
{
"page": "User talk:Dudeperson176123",
"Edits": 18
},
{
"page": "Wikipédia:Le Bistro/12 septembre 2015",
"Edits": 18
},
{
"page": "Wikipedia:In the news/Candidates",
"Edits": 17
},
{
"page": "Wikipedia:Requests for page protection",
"Edits": 17
}
]
```
#### 更多Druid SQL示例
这是一组可尝试的查询:
**时间查询**
```
SELECT FLOOR(__time to HOUR) AS HourTime, SUM(deleted) AS LinesDeleted
FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00'
GROUP BY 1
```
![](img-3/tutorial-query-03.png)
**聚合查询**
```
SELECT channel, page, SUM(added)
FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00'
GROUP BY channel, page
ORDER BY SUM(added) DESC
```
![](img-3/tutorial-query-04.png)
**查询原始数据**
```
SELECT user, page
FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 02:00:00' AND TIMESTAMP '2015-09-12 03:00:00'
LIMIT 5
```
![](img-3/tutorial-query-05.png)
#### SQL查询计划
Druid SQL能够解释给定查询的查询计划, 在控制台中,可以通过 `...` 按钮访问此功能。
![](img-3/tutorial-query-06.png)
如果您以其他方式查询则可以通过在Druid SQL查询之前添加 `EXPLAIN PLAN FOR` 来获得查询计划。
使用上边的一个示例:
`EXPLAIN PLAN FOR SELECT page, COUNT(*) AS Edits FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00' GROUP BY page ORDER BY Edits DESC LIMIT 10;`
```
dsql> EXPLAIN PLAN FOR SELECT page, COUNT(*) AS Edits FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00' GROUP BY page ORDER BY Edits DESC LIMIT 10;
┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ PLAN │
├─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
│ DruidQueryRel(query=[{"queryType":"topN","dataSource":{"type":"table","name":"wikipedia"},"virtualColumns":[],"dimension":{"type":"default","dimension":"page","outputName":"d0","outputType":"STRING"},"metric":{"type":"numeric","metric":"a0"},"threshold":10,"intervals":{"type":"intervals","intervals":["2015-09-12T00:00:00.000Z/2015-09-13T00:00:00.001Z"]},"filter":null,"granularity":{"type":"all"},"aggregations":[{"type":"count","name":"a0"}],"postAggregations":[],"context":{},"descending":false}], signature=[{d0:STRING, a0:LONG}]) │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
Retrieved 1 row in 0.03s.
```
### 原生JSON查询
Druid的原生查询格式以JSON表示。
#### 通过控制台原生查询
您可以从控制台的"Query"视图发出原生Druid查询。
这是一个查询可检索2015-09-12上具有最多页面编辑量的10个wikipedia页面。
```
{
"queryType" : "topN",
"dataSource" : "wikipedia",
"intervals" : ["2015-09-12/2015-09-13"],
"granularity" : "all",
"dimension" : "page",
"metric" : "count",
"threshold" : 10,
"aggregations" : [
{
"type" : "count",
"name" : "count"
}
]
}
```
只需将其粘贴到控制台即可将编辑器切换到JSON模式。
![](img-3/tutorial-query-07.png)
#### 通过HTTP原生查询
我们在 `quickstart/tutorial/wikipedia-top-pages.json` 文件中包括了一个示例原生TopN查询。
提交该查询到Druid
```
curl -X 'POST' -H 'Content-Type:application/json' -d @quickstart/tutorial/wikipedia-top-pages.json http://localhost:8888/druid/v2?pretty
```
您可以看到如下的查询结果:
```
[ {
"timestamp" : "2015-09-12T00:46:58.771Z",
"result" : [ {
"count" : 33,
"page" : "Wikipedia:Vandalismusmeldung"
}, {
"count" : 28,
"page" : "User:Cyde/List of candidates for speedy deletion/Subpage"
}, {
"count" : 27,
"page" : "Jeremy Corbyn"
}, {
"count" : 21,
"page" : "Wikipedia:Administrators' noticeboard/Incidents"
}, {
"count" : 20,
"page" : "Flavia Pennetta"
}, {
"count" : 18,
"page" : "Total Drama Presents: The Ridonculous Race"
}, {
"count" : 18,
"page" : "User talk:Dudeperson176123"
}, {
"count" : 18,
"page" : "Wikipédia:Le Bistro/12 septembre 2015"
}, {
"count" : 17,
"page" : "Wikipedia:In the news/Candidates"
}, {
"count" : 17,
"page" : "Wikipedia:Requests for page protection"
} ]
} ]
```
### 进一步阅读
[查询文档]()有更多关于Druid原生JSON查询的信息
[Druid SQL文档]()有更多关于Druid SQL查询的信息