ydb/yql/essentials/docs/en/syntax/export_import.md

Putting part of the query into a separate file

Here's the mechanism for putting part of the query into a separate attached file:

• PRAGMA Library marks the attached file as available for import.

Export

• EXPORT $my_symbol1, $my_symbol2, ...; lists the names of named expressions in the library that are available for import.

Import

• IMPORT my_library SYMBOLS $my_symbol1, $my_symbol2, ...; makes the listed named expressions available for further use.

{% note info %}

You can use the library to include lambdas, actions, named subqueries, constants and expressions, but not subqueries or aggregate functions.

{% endnote %}

{% note warning %}

The file linked by the PRAGMA Library must be attached to the query. You can't use a PRAGMA File for this purpose.

{% endnote %}

Examples

my_lib.sql:

$Square = ($x) -> { RETURN $x * $x; };
$Sqrt = ($x) -> { RETURN Math::Sqrt($x); };

-- Aggregate functions created by
-- AggregationFactory, it makes sense to add it to the library
$Agg_sum = AggregationFactory("SUM");
$Agg_max = AggregationFactory("MAX");

EXPORT $Square, $Sqrt, $Agg_sum, $Agg_max;

Query:

PRAGMA Library("my_lib.sql");
IMPORT my_lib SYMBOLS $Square, $Sqrt, $Agg_sum, $Agg_max;
SELECT
  $Square(2), -- 4
  $Sqrt(4);   -- 2

SELECT
  AGGREGATE_BY(x, $Agg_sum), -- 5
  AGGREGATE_BY(x, $Agg_max)  -- 3
FROM (
  SELECT 2 AS x
  UNION ALL
  SELECT 3 AS x
)