DESCRIBE QUERY

Returnerar metadata för utdata från en fråga.

Syntax

{ DESC | DESCRIBE } [ QUERY ] input_statement

Parametrar

  • Fråga Denna sats är valfri och kan utelämnas.

  • input_statement

    En resultat uppsättning som genererar uttryck och kan vara något av följande:

    • en SELECT instruktion
    • en CTE(Common table expression) instruktion
    • en INLINE TABLE instruktion
    • en TABLE instruktion
    • en FROM instruktion '

    Se SELECT-satsen för en detaljerad syntax för Frågeparametern.

Exempel

-- 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|
+--------+---------+----------+