Query data

Query data

This tutorial demonstrates how to query data in Apache Druid using SQL.

It assumes that you’ve completed the Quickstart or one of the following tutorials, since we’ll query datasources that you would have created by following one of them:

There are various ways to run Druid SQL queries: from the web console, using a command line utility and by posting the query by HTTP. We’ll look at each of these.

Query SQL from the web console

The web console includes a view that makes it easier to build and test queries, and view their results.

Start up the Druid cluster, if it’s not already running, and open the web console in your web browser.
Click Query from the header to open the Query view:

You can always write queries directly in the edit pane, but the Query view also provides facilities to help you construct SQL queries, which we will use to generate a starter query.
Expand the wikipedia datasource tree in the left pane. We’ll create a query for the page dimension.
Click page and then Show:page from the menu:

A SELECT query appears in the query edit pane and immediately runs. However, in this case, the query returns no data, since by default the query filters for data from the last day, while our data is considerably older than that. Let’s remove the filter.
Click Run to run the query.

You should now see two columns of data, a page name and the count:

Notice that the results are limited in the console to about a hundred, by default, due to the Smart query limit feature. This helps users avoid inadvertently running queries that return an excessive amount of data, possibly overwhelming their system.
Let’s edit the query directly and take a look at a few more query building features in the editor. Click in the query edit pane and make the following changes:
1. Add a line after the first column, "page" and Start typing the name of a new column, "countryName". Notice that the autocomplete menu suggests column names, functions, keywords, and more. Choose “countryName” and add the new column to the GROUP BY clause as well, either by name or by reference to its position, 2.
2. For readability, replace Count column name with Edits, since the COUNT() function actually returns the number of edits for the page. Make the same column name change in the ORDER BY clause as well.
```
  The `COUNT()` function is one of many functions available for use in Druid SQL queries. You can mouse over a function name
  in the autocomplete menu to see a brief description of a function. Also, you can find more information in the Druid 
  documentation; for example, the `COUNT()` function is documented in 
  [Aggregation functions](/docs/29.0.1/querying/sql-aggregations).
```
  The query should now be:
```
SELECT
  "page",
  "countryName",
  COUNT(*) AS "Edits"
FROM "wikipedia"
GROUP BY 1, 2
ORDER BY "Edits" DESC
```
  When you run the query again, notice that we’re getting the new dimension,countryName, but for most of the rows, its value is null. Let’s show only rows with a countryName value.
Click the countryName dimension in the left pane and choose the first filtering option. It’s not exactly what we want, but we’ll edit it by hand. The new WHERE clause should appear in your query.
Modify the WHERE clause to exclude results that do not have a value for countryName:
```
WHERE "countryName" IS NOT NULL
```
Run the query again. You should now see the top edits by country:
Under the covers, every Druid SQL query is translated into a query in the JSON-based Druid native query format before it runs on data nodes. You can view the native query for this query by clicking ... and Explain SQL Query.

While you can use Druid SQL for most purposes, familiarity with native query is useful for composing complex queries and for troubleshooting performance issues. For more information, see Native queries.

info

Another way to view the explain plan is by adding EXPLAIN PLAN FOR to the front of your query, as follows:

EXPLAIN PLAN FOR
SELECT
  "page",
  "countryName",
  COUNT(*) AS "Edits"
FROM "wikipedia"
WHERE "countryName" IS NOT NULL
GROUP BY 1, 2
ORDER BY "Edits" DESC

This is particularly useful when running queries from the command line or over HTTP.

Finally, click ... and Edit context to see how you can add additional parameters controlling the execution of the query execution. In the field, enter query context options as JSON key-value pairs, as described in Context flags.

That’s it! We’ve built a simple query using some of the query builder features built into the web console. The following sections provide a few more example queries you can try.

See Query SQL over HTTP for an example of how to use the Druid SQL HTTP API.

More Druid SQL examples

Try the following queries to learn a few more Druid SQL tricks:

Query over time

SELECT FLOOR(__time to HOUR) AS HourTime, SUM(deleted) AS LinesDeleted
FROM wikipedia WHERE TIME_IN_INTERVAL("__time", '2016-06-27/2016-06-28')
GROUP BY 1

General group by

SELECT channel, page, SUM(added)
FROM wikipedia WHERE TIME_IN_INTERVAL("__time", '2016-06-27/2016-06-28')
GROUP BY channel, page
ORDER BY SUM(added) DESC

Query SQL over HTTP

You can submit native queries directly to the Druid Broker over HTTP. The request body should be a JSON object, with the value for the key query containing text of the query:

{
  "query": "SELECT page, COUNT(*) AS Edits FROM wikipedia WHERE TIME_IN_INTERVAL(\"__time\", '2016-06-27/2016-06-28') GROUP BY page ORDER BY Edits DESC LIMIT 10"
}

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:

curl -X 'POST' -H 'Content-Type:application/json' -d @quickstart/tutorial/wikipedia-top-pages-sql.json http://localhost:8888/druid/v2/sql

The following results should be returned:

[
    {
        "page": "Copa América Centenario",
        "Edits": 29
    },
    {
        "page": "User:Cyde/List of candidates for speedy deletion/Subpage",
        "Edits": 16
    },
    {
        "page": "Wikipedia:Administrators' noticeboard/Incidents",
        "Edits": 16
    },
    {
        "page": "2016 Wimbledon Championships – Men's Singles",
        "Edits": 15
    },
    {
        "page": "Wikipedia:Administrator intervention against vandalism",
        "Edits": 15
    },
    {
        "page": "Wikipedia:Vandalismusmeldung",
        "Edits": 15
    },
    {
        "page": "The Winds of Winter (Game of Thrones)",
        "Edits": 12
    },
    {
        "page": "ولاية الجزائر",
        "Edits": 12
    },
    {
        "page": "Copa América",
        "Edits": 10
    },
    {
        "page": "Lionel Messi",
        "Edits": 10
    }
]

Query data

Query data

Query SQL from the web console

More Druid SQL examples

Query over time

General group by

Query SQL over HTTP

Further reading