16.11. DESCRIBE OUTPUT

Synopsis

DESCRIBE OUTPUT statement_name

Description

Describes the output columns of a prepared statement. It returns a table with metadata about each output column. Each row in the output provides the following information: column name (or the column’s alias if it is aliased), table, schema, connector, type, type size in bytes, boolean indicating whether the column is aliased and boolean indicating whether the query is a row count query (DDL/DML query that returns no data). For more information on preparing a statement see PREPARE.

Examples

1. Describe a query with four output columns:

   Let my_select be the name of the prepared statement SELECT * FROM nation:

   DESCRIBE OUTPUT my_select;
   

   Returns a table with metadata on all output columns

    Column Name | Table  | Schema | Connector |  Type   | Type Size | Aliased | Row Count Query
   -------------+--------+--------+-----------+---------+-----------+---------+-----------------
    nationkey   | nation | sf1    | tpch      | bigint  |         8 | false   | false
    name        | nation | sf1    | tpch      | varchar |         0 | false   | false
    regionkey   | nation | sf1    | tpch      | bigint  |         8 | false   | false
    comment     | nation | sf1    | tpch      | varchar |         0 | false   | false
   

2. Describe a query whose output columns are expressions:

   Let my_select be the name of the prepared statement SELECT count(*) as my_count, 1+2 FROM nation:

   DESCRIBE OUTPUT my_select;
   

   Returns a table with two rows

    Column Name | Table | Schema | Connector |  Type  | Type Size | Aliased | Row Count Query
   -------------+-------+--------+-----------+--------+-----------+---------+-----------------
    my_count    |       |        |           | bigint |         8 | true    | false
    _col1       |       |        |           | bigint |         8 | false   | false
   

3. Describe a row count query:

   Let my_show_tables be the name of the prepared statement show tables:

   DESCRIBE OUTPUT my_show_tables;
   

   Returns a table with one null row

    Column Name | Table | Schema | Connector | Type | Type Size | Aliased | Row Count Query
   -------------+-------+--------+-----------+------+-----------+---------+-----------------
    NULL        | NULL  | NULL   | NULL      | NULL | NULL      | NULL    | true