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306 lines
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Markdown
306 lines
15 KiB
Markdown
---
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layout: doc_page
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title: "Tutorial: Querying data"
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---
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# Tutorial: Querying data
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This tutorial will demonstrate how to query data in Apache Druid (incubating), with examples for Druid SQL and Druid's native query format.
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The tutorial assumes that you've already completed one of the 4 ingestion tutorials, as we will be querying the sample Wikipedia edits data.
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* [Tutorial: Loading a file](../tutorials/tutorial-batch.html)
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* [Tutorial: Loading stream data from Kafka](../tutorials/tutorial-kafka.html)
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* [Tutorial: Loading a file using Hadoop](../tutorials/tutorial-batch-hadoop.html)
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* [Tutorial: Loading stream data using Tranquility](../tutorials/tutorial-tranquility.html)
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Druid queries are sent over HTTP.
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The Druid console includes a view to issue queries to Druid and nicely format the results.
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## Druid SQL queries
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Druid supports a dialect of SQL for querying.
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This query retrieves the 10 Wikipedia pages with the most page edits on 2015-09-12.
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```sql
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SELECT page, COUNT(*) AS Edits
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FROM wikipedia
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WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00'
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GROUP BY page ORDER BY Edits DESC
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LIMIT 10
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```
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Let's look at the different ways to issue this query.
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### Query SQL via the console
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You can issue the above query from the console.
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The console query view provides autocomplete together with inline function documentation.
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You can also configure extra context flags to be sent with the query from the more options menu.
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Note that the console will by default wrap your SQL queries in a limit so that you can issue queries like `SELECT * FROM wikipedia` without much hesitation - you can turn off this behaviour.
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### Query SQL via dsql
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For convenience, the Druid package includes a SQL command-line client, located at `bin/dsql` from the Druid package root.
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Let's now run `bin/dsql`; you should see the following prompt:
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```bash
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Welcome to dsql, the command-line client for Druid SQL.
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Type "\h" for help.
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dsql>
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```
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To submit the query, paste it to the `dsql` prompt and press enter:
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```bash
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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;
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┌──────────────────────────────────────────────────────────┬───────┐
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│ page │ Edits │
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├──────────────────────────────────────────────────────────┼───────┤
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│ Wikipedia:Vandalismusmeldung │ 33 │
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│ User:Cyde/List of candidates for speedy deletion/Subpage │ 28 │
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│ Jeremy Corbyn │ 27 │
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│ Wikipedia:Administrators' noticeboard/Incidents │ 21 │
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│ Flavia Pennetta │ 20 │
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│ Total Drama Presents: The Ridonculous Race │ 18 │
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│ User talk:Dudeperson176123 │ 18 │
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│ Wikipédia:Le Bistro/12 septembre 2015 │ 18 │
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│ Wikipedia:In the news/Candidates │ 17 │
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│ Wikipedia:Requests for page protection │ 17 │
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└──────────────────────────────────────────────────────────┴───────┘
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Retrieved 10 rows in 0.06s.
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```
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### Query SQL over HTTP
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The SQL queries are submitted as JSON over HTTP.
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The tutorial package includes an example file that contains the SQL query shown above at `quickstart/tutorial/wikipedia-top-pages-sql.json`. Let's submit that query to the Druid Broker:
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```bash
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curl -X 'POST' -H 'Content-Type:application/json' -d @quickstart/tutorial/wikipedia-top-pages-sql.json http://localhost:8888/druid/v2/sql
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```
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The following results should be returned:
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```json
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[
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{
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"page": "Wikipedia:Vandalismusmeldung",
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"Edits": 33
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},
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{
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"page": "User:Cyde/List of candidates for speedy deletion/Subpage",
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"Edits": 28
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},
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{
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"page": "Jeremy Corbyn",
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"Edits": 27
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},
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{
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"page": "Wikipedia:Administrators' noticeboard/Incidents",
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"Edits": 21
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},
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{
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"page": "Flavia Pennetta",
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"Edits": 20
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},
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{
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"page": "Total Drama Presents: The Ridonculous Race",
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"Edits": 18
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},
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{
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"page": "User talk:Dudeperson176123",
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"Edits": 18
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},
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{
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"page": "Wikipédia:Le Bistro/12 septembre 2015",
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"Edits": 18
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},
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{
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"page": "Wikipedia:In the news/Candidates",
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"Edits": 17
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},
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{
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"page": "Wikipedia:Requests for page protection",
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"Edits": 17
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}
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]
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```
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### More Druid SQL examples
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Here is a collection of queries to try out:
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#### Query over time
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```sql
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SELECT FLOOR(__time to HOUR) AS HourTime, SUM(deleted) AS LinesDeleted
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FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00'
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GROUP BY 1
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```
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#### General group by
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```sql
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SELECT channel, page, SUM(added)
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FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 00:00:00' AND TIMESTAMP '2015-09-13 00:00:00'
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GROUP BY channel, page
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ORDER BY SUM(added) DESC
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```
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#### Select raw data
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```sql
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SELECT user, page
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FROM wikipedia WHERE "__time" BETWEEN TIMESTAMP '2015-09-12 02:00:00' AND TIMESTAMP '2015-09-12 03:00:00'
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LIMIT 5
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```
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### Explain query plan
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Druid SQL has the ability to explain the query plan for a given query.
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In the console this functionality is accessible from the `...` button.
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If you are querying in other ways you can get the plan by prepending `EXPLAIN PLAN FOR ` to a Druid SQL query.
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Using a query from an example above:
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`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;`
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```bash
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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;
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┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
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│ PLAN │
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├─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┤
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│ 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}]) │
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└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
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Retrieved 1 row in 0.03s.
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```
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## Native JSON queries
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Druid's native query format is expressed in JSON.
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### Native query via the console
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You can issue native Druid queries from the console's Query view.
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Here is a query that retrieves the 10 Wikipedia pages with the most page edits on 2015-09-12.
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```json
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{
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"queryType" : "topN",
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"dataSource" : "wikipedia",
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"intervals" : ["2015-09-12/2015-09-13"],
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"granularity" : "all",
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"dimension" : "page",
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"metric" : "count",
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"threshold" : 10,
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"aggregations" : [
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{
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"type" : "count",
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"name" : "count"
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}
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]
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}
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```
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Simply paste it into the console to switch the editor into JSON mode.
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### Native queries over HTTP
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We have included a sample native TopN query under `quickstart/tutorial/wikipedia-top-pages.json`:
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Let's submit this query to Druid:
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```bash
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curl -X 'POST' -H 'Content-Type:application/json' -d @quickstart/tutorial/wikipedia-top-pages.json http://localhost:8888/druid/v2?pretty
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```
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You should see the following query results:
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```json
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[ {
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"timestamp" : "2015-09-12T00:46:58.771Z",
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"result" : [ {
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"count" : 33,
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"page" : "Wikipedia:Vandalismusmeldung"
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}, {
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"count" : 28,
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"page" : "User:Cyde/List of candidates for speedy deletion/Subpage"
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}, {
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"count" : 27,
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"page" : "Jeremy Corbyn"
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}, {
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"count" : 21,
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"page" : "Wikipedia:Administrators' noticeboard/Incidents"
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}, {
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"count" : 20,
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"page" : "Flavia Pennetta"
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}, {
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"count" : 18,
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"page" : "Total Drama Presents: The Ridonculous Race"
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}, {
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"count" : 18,
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"page" : "User talk:Dudeperson176123"
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}, {
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"count" : 18,
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"page" : "Wikipédia:Le Bistro/12 septembre 2015"
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}, {
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"count" : 17,
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"page" : "Wikipedia:In the news/Candidates"
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}, {
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"count" : 17,
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"page" : "Wikipedia:Requests for page protection"
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} ]
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} ]
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```
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## Further reading
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The [Queries documentation](../querying/querying.html) has more information on Druid's native JSON queries.
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The [Druid SQL documentation](../querying/sql.html) has more information on using Druid SQL queries.
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