DESCRIBE FUNCTION
描述
DESCRIBE FUNCTION 语句返回现有函数的基本元数据信息。元数据信息包括函数名称、实现类和使用详情。如果指定了可选的 EXTENDED 选项，则会返回基本元数据信息以及扩展使用信息。
语法
{ DESC | DESCRIBE } FUNCTION [ EXTENDED ] function_name
参数
-
function_name
指定系统中现有函数的名称。函数名称可以选择使用数据库名称进行限定。如果
function_name使用数据库进行限定，则从用户指定的数据库解析函数，否则从当前数据库解析函数。语法：
[ database_name. ] function_name
示例
-- 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 |
+---------------------------------------------------------------+