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https://issues.apache.org/jira/browse/DRILL-7861?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Cong Luo resolved DRILL-7861.
-----------------------------
Reviewer: Cong Luo
Resolution: Fixed
> Add Function to Obtain Inner Map Schemata
> -----------------------------------------
>
> Key: DRILL-7861
> URL: https://issues.apache.org/jira/browse/DRILL-7861
> Project: Apache Drill
> Issue Type: Improvement
> Components: Metadata
> Affects Versions: 1.18.0
> Reporter: Charles Givre
> Assignee: Charles Givre
> Priority: Major
> Fix For: 1.19.0
>
>
> This function allows you to drill down into the schema of maps. The REST API
> and JDBC interfaces will only return `MAP`, `LIST` for the MAP, however, it
> is not possible to get
> the schema of the inner map. The function `getMapSchema(<MAP>)` will return a
> `MAP` of the fields and datatypes.
> ### Example Usage
> Using the data below, the query below will return the schema as shown below.
> ```bash
> apache drill> SELECT getMapSchema(record) AS schema FROM
> dfs.test.`schema_test.json`;
> +----------------------------------------------------------------------------------+
> | schema
> |
> +----------------------------------------------------------------------------------+
> |
> {"int_field":"BIGINT","double_field":"FLOAT8","string_field":"VARCHAR","int_list":"REPEATED_BIGINT","double_list":"REPEATED_FLOAT8","map":"MAP"}
> |
> +----------------------------------------------------------------------------------+
> 1 row selected (0.298 seconds)
> ```
> ```json
> {
> "record" : {
> "int_field": 1,
> "double_field": 2.0,
> "string_field": "My string",
> "int_list": [1,2,3],
> "double_list": [1.0,2.0,3.0],
> "map": {
> "nested_int_field" : 5,
> "nested_double_field": 5.0,
> "nested_string_field": "5.0"
> }
> },
> "single_field": 10
> }
> ```
> The function returns an empty map if the row is `null`.
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