DESCRIBE QUERYDESCRIBE QUERY

返回查询输出的元数据。Returns the metadata of output of a query.

语法Syntax

{ DESC | DESCRIBE } [ QUERY ] input_statement

参数Parameters

  • QUERY 此子句是可选的,并可以省略。QUERY This clause is optional and may be omitted.

  • input_statementinput_statement

    生成语句的结果集,可以是以下内容之一:A result set producing statement and may be one of the following:

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

    有关查询参数的详细语法,请参阅 select-statementRefer to select-statement for a detailed syntax of the query parameter.

示例Examples

-- 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 expression (`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 an 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| Agecolumn|
| 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| Agecolumn|
+--------+---------+----------+