mirror of
https://github.com/apache/druid.git
synced 2025-03-02 07:19:14 +00:00
d007477742
* Docusaurus build framework + ingestion doc refresh. * stick to npm instead of yarn * fix typos * restore some _bin * Adjustments. * detect and fix redirect anchors * update anchor lint * Web-console: remove specific column filters (#8343) * add clear filter * update tool kit * remove usless check * auto run * add % * Fix resource leak (#8337) * Fix resource leak * Patch comments * Enable Spotbugs NP_NONNULL_RETURN_VIOLATION (#8234) * Fixes from PR review. * Fix more anchors. * Preamble nix. * Fix more anchors, headers * clean up placeholder page * add to website lint to travis config * better broken link checking * travis fix * Fixed more broken links * better redirects * unfancy catch * fix LGTM error * link fixes * fix md issues * Addl fixes
80 lines
2.3 KiB
Markdown
80 lines
2.3 KiB
Markdown
---
|
|
id: virtual-columns
|
|
title: "Virtual Columns"
|
|
---
|
|
|
|
<!--
|
|
~ 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.
|
|
-->
|
|
|
|
|
|
Virtual columns are queryable column "views" created from a set of columns during a query.
|
|
|
|
A virtual column can potentially draw from multiple underlying columns, although a virtual column always presents itself as a single column.
|
|
|
|
Virtual columns can be used as dimensions or as inputs to aggregators.
|
|
|
|
Each Apache Druid (incubating) query can accept a list of virtual columns as a parameter. The following scan query is provided as an example:
|
|
|
|
```
|
|
{
|
|
"queryType": "scan",
|
|
"dataSource": "page_data",
|
|
"columns":[],
|
|
"virtualColumns": [
|
|
{
|
|
"type": "expression",
|
|
"name": "fooPage",
|
|
"expression": "concat('foo' + page)",
|
|
"outputType": "STRING"
|
|
},
|
|
{
|
|
"type": "expression",
|
|
"name": "tripleWordCount",
|
|
"expression": "wordCount * 3",
|
|
"outputType": "LONG"
|
|
}
|
|
],
|
|
"intervals": [
|
|
"2013-01-01/2019-01-02"
|
|
]
|
|
}
|
|
```
|
|
|
|
|
|
## Virtual column types
|
|
|
|
### Expression virtual column
|
|
|
|
The expression virtual column has the following syntax:
|
|
|
|
```
|
|
{
|
|
"type": "expression",
|
|
"name": <name of the virtual column>,
|
|
"expression": <row expression>,
|
|
"outputType": <output value type of expression>
|
|
}
|
|
```
|
|
|
|
|property|description|required?|
|
|
|--------|-----------|---------|
|
|
|name|The name of the virtual column.|yes|
|
|
|expression|An [expression](../misc/math-expr.md) that takes a row as input and outputs a value for the virtual column.|yes|
|
|
|outputType|The expression's output will be coerced to this type. Can be LONG, FLOAT, DOUBLE, or STRING.|no, default is FLOAT|
|