f96486b4aa
### What changes were proposed in this pull request? Document SHOW FUNCTIONS statement in SQL Reference Guide. ### Why are the changes needed? Currently Spark lacks documentation on the supported SQL constructs causing confusion among users who sometimes have to look at the code to understand the usage. This is aimed at addressing this issue. ### Does this PR introduce any user-facing change? Yes. **Before:** There was no documentation for this. **After.**  <img width="589" alt="Screen Shot 2019-09-04 at 11 41 44 AM" src="https://user-images.githubusercontent.com/11567269/64281911-0fe79000-cf09-11e9-955f-21b44590707c.png"> <img width="572" alt="Screen Shot 2019-09-04 at 11 41 54 AM" src="https://user-images.githubusercontent.com/11567269/64281916-12e28080-cf09-11e9-9187-688c2c751559.png"> ### How was this patch tested? Tested using jykyll build --serve Closes #25539 from dilipbiswal/ref-doc-show-functions. Lead-authored-by: Dilip Biswal <dbiswal@us.ibm.com> Co-authored-by: Xiao Li <gatorsmile@gmail.com> Signed-off-by: Xiao Li <gatorsmile@gmail.com>
5.3 KiB
| layout | title | displayTitle | license |
|---|---|---|---|
| global | DESCRIBE FUNCTION | DESCRIBE FUNCTION | 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
DESCRIBE FUNCTION statement returns the basic metadata information of an
existing function. The metadata information includes the function name, implementing
class and the usage details. If the optional EXTENDED option is specified, the basic
metadata information is returned along with the extended usage information.
Syntax
{% highlight sql %} {DESC | DESCRIBE} FUNCTION [EXTENDED] function_name {% endhighlight %}
Parameters
function_name-
Specifies a name of an existing function in the system. The function name may be
optionally qualified with a database name. If `function_name` is qualified with
a database then the function is resolved from the user specified database, otherwise
it is resolved from the current database.
Syntax:[database_name.]function_name
Examples
{% highlight sql %} -- Describe a builtin scalar function. -- Returns function name, implementing class and usage DESC FUNCTION abs; +-------------------------------------------------------------------+ |function_desc | +-------------------------------------------------------------------+ |Function: abs | |Class: org.apache.spark.sql.catalyst.expressions.Abs | |Usage: abs(expr) - Returns the absolute value of the numeric value.| +-------------------------------------------------------------------+
-- Describe a builtin scalar function. -- Returns function name, implementing class and usage and examples. DESC FUNCTION EXTENDED abs; +-------------------------------------------------------------------+ |function_desc | +-------------------------------------------------------------------+ |Function: abs | |Class: org.apache.spark.sql.catalyst.expressions.Abs | |Usage: abs(expr) - Returns the absolute value of the numeric value.| |Extended Usage: | | Examples: | | > SELECT abs(-1); | | 1 | | | +-------------------------------------------------------------------+
-- Describe a builtin aggregate function
DESC FUNCTION max;
+--------------------------------------------------------------+
|function_desc |
+--------------------------------------------------------------+
|Function: max |
|Class: org.apache.spark.sql.catalyst.expressions.aggregate.Max|
|Usage: max(expr) - Returns the maximum value of expr. |
+--------------------------------------------------------------+
-- Describe a builtin user defined aggregate function
-- Returns function name, implementing class and usage and examples.
DESC FUNCTION EXTENDED explode
+---------------------------------------------------------------+
|function_desc |
+---------------------------------------------------------------+
|Function: explode |
|Class: org.apache.spark.sql.catalyst.expressions.Explode |
|Usage: explode(expr) - Separates the elements of array expr |
| into multiple rows, or the elements of map expr into |
| multiple rows and columns. Unless specified otherwise, uses |
| the default column name col for elements of the array or |
| key and value for the elements of the map. |
|Extended Usage: |
| Examples: |
| > SELECT explode(array(10, 20)); |
| 10 |
| 20 |
+---------------------------------------------------------------+
{% endhighlight %}