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doc_page	Tutorial: Querying data

Tutorial: Querying data

This tutorial will demonstrate how to query data in Druid, with examples for Druid's native query format and Druid SQL.

The tutorial assumes that you've already completed one of the 4 ingestion tutorials, as we will be querying the sample Wikipedia edits data.

Native JSON queries

Druid's native query format is expressed in JSON. We have included a sample native TopN query under quickstart/tutorial/wikipedia-top-pages.json:

{
  "queryType" : "topN",
  "dataSource" : "wikipedia",
  "intervals" : ["2015-09-12/2015-09-13"],
  "granularity" : "all",
  "dimension" : "page",
  "metric" : "count",
  "threshold" : 10,
  "aggregations" : [
    {
      "type" : "count",
      "name" : "count"
    }
  ]
}

This query retrieves the 10 Wikipedia pages with the most page edits on 2015-09-12.

Let's submit this query to the Druid broker:

curl -X 'POST' -H 'Content-Type:application/json' -d @quickstart/tutorial/wikipedia-top-pages.json http://localhost:8082/druid/v2?pretty

You should see the following query results:

[ {
  "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"
  } ]
} ]

Druid SQL queries

Druid also supports a dialect of SQL for querying. Let's run a SQL query that is equivalent to the native JSON query shown above:

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;

The SQL queries are submitted as JSON over HTTP.

TopN query example

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:8082/druid/v2/sql

The following results should be returned:

[
  {
    "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
  }
]

dsql client

For convenience, the Druid package includes a SQL command-line client, located at bin/dsql from the Druid package root.

Let's now run bin/dsql; you should see the following prompt:

Welcome to dsql, the command-line client for Druid SQL.
Type "\h" for help.
dsql>

To submit the query, paste it to the dsql prompt and press enter:

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.

Additional Druid SQL queries

Timeseries

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 FLOOR(__time to HOUR);

dsql> 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 FLOOR(__time to HOUR);
┌──────────────────────────┬──────────────┐
│ HourTime                 │ LinesDeleted │
├──────────────────────────┼──────────────┤
│ 2015-09-12T00:00:00.000Z │         1761 │
│ 2015-09-12T01:00:00.000Z │        16208 │
│ 2015-09-12T02:00:00.000Z │        14543 │
│ 2015-09-12T03:00:00.000Z │        13101 │
│ 2015-09-12T04:00:00.000Z │        12040 │
│ 2015-09-12T05:00:00.000Z │         6399 │
│ 2015-09-12T06:00:00.000Z │         9036 │
│ 2015-09-12T07:00:00.000Z │        11409 │
│ 2015-09-12T08:00:00.000Z │        11616 │
│ 2015-09-12T09:00:00.000Z │        17509 │
│ 2015-09-12T10:00:00.000Z │        19406 │
│ 2015-09-12T11:00:00.000Z │        16284 │
│ 2015-09-12T12:00:00.000Z │        18672 │
│ 2015-09-12T13:00:00.000Z │        30520 │
│ 2015-09-12T14:00:00.000Z │        18025 │
│ 2015-09-12T15:00:00.000Z │        26399 │
│ 2015-09-12T16:00:00.000Z │        24759 │
│ 2015-09-12T17:00:00.000Z │        19634 │
│ 2015-09-12T18:00:00.000Z │        17345 │
│ 2015-09-12T19:00:00.000Z │        19305 │
│ 2015-09-12T20:00:00.000Z │        22265 │
│ 2015-09-12T21:00:00.000Z │        16394 │
│ 2015-09-12T22:00:00.000Z │        16379 │
│ 2015-09-12T23:00:00.000Z │        15289 │
└──────────────────────────┴──────────────┘
Retrieved 24 rows in 0.08s.

GroupBy

SELECT channel, 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 ORDER BY SUM(added) DESC LIMIT 5;

dsql> SELECT channel, 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 ORDER BY SUM(added) DESC LIMIT 5;
┌───────────────┬─────────┐
│ channel       │ EXPR$1  │
├───────────────┼─────────┤
│ #en.wikipedia │ 3045299 │
│ #it.wikipedia │  711011 │
│ #fr.wikipedia │  642555 │
│ #ru.wikipedia │  640698 │
│ #es.wikipedia │  634670 │
└───────────────┴─────────┘
Retrieved 5 rows in 0.05s.

Scan

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;

 dsql> 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;
┌────────────────────────┬────────────────────────────────────────────────────────┐
│ user                   │ page                                                   │
├────────────────────────┼────────────────────────────────────────────────────────┤
│ Thiago89               │ Campeonato Mundial de Voleibol Femenino Sub-20 de 2015 │
│ 91.34.200.249          │ Friede von Schönbrunn                                  │
│ TuHan-Bot              │ Trĩ vàng                                               │
│ Lowercase sigmabot III │ User talk:ErrantX                                      │
│ BattyBot               │ Hans W. Jung                                           │
└────────────────────────┴────────────────────────────────────────────────────────┘
Retrieved 5 rows in 0.04s.

EXPLAIN PLAN FOR

By prepending EXPLAIN PLAN FOR to a Druid SQL query, it is possible to see what native Druid queries a SQL query will plan into.

Using the TopN query above as an example:

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.

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