spark-instrumented-optimizer/docs/sql-ref-syntax-aux-describe-query.md

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global	DESCRIBE QUERY	DESCRIBE QUERY	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.

Description

The DESCRIBE QUERY statement is used to return the metadata of output of a query. A shorthand DESC may be used instead of DESCRIBE to describe the query output.

Syntax

{% highlight sql %} {DESC | DESCRIBE} [QUERY] input_statement {% endhighlight %}

Parameters

QUERY

This clause is optional and may be omitted.

input_statement

Specifies a result set producing statement and may be one of the following:

• a SELECT statement
• a CTE(Common table expression) statement
• an INLINE TABLE statement
• a TABLE statement
• a FROM statement

Please refer to select-statement for a detailed syntax of the query parameter.

Examples

{% highlight sql %} -- Create table person CREATE TABLE person (name STRING , age INT COMMENT 'Age column', address STRING);

-- Returns column metadata information for a simple select query DESCRIBE QUERY select age, sum(age) FROM person GROUP BY age; +--------+---------+----------+ |col_name|data_type|comment | +--------+---------+----------+ |age |int |Age column| |sum(age)|bigint |null | +--------+---------+----------+

-- Returns column metadata information for common table experession (CTE). DESCRIBE QUERY WITH all_names_cte AS (SELECT name from person) SELECT * FROM all_names_cte; +--------+---------+-------+ |col_name|data_type|comment| +--------+---------+-------+ |name |string |null | +--------+---------+-------+

-- Returns column metadata information for a inline table. DESC QUERY VALUES(100, 'John', 10000.20D) AS employee(id, name, salary); +--------+---------+-------+ |col_name|data_type|comment| +--------+---------+-------+ |id |int |null | |name |string |null | |salary |double |null | +--------+---------+-------+

-- Returns column metadata information for TABLE statement. DESC QUERY TABLE person; +--------+---------+----------+ |col_name|data_type|comment | +--------+---------+----------+ |name |string |null | |age |int |Age column| |address |string |null | +--------+---------+----------+

-- Returns column metadata information for a FROM statement. -- QUERY clause is optional and can be omitted. DESCRIBE FROM person SELECT age; +--------+---------+----------+ |col_name|data_type|comment | +--------+---------+----------+ |age |int |Age column| +--------+---------+----------+ {% endhighlight %}

Related Statements

• DESCRIBE DATABASE
• DESCRIBE TABLE
• DESCRIBE FUNCTION