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

Lambdas, actions, named subqueries, constant values, and expressions can be transferred to the library, but subqueries or aggregate functions cannot be.

Warning

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

Examples:

my_lib.sql:

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

-- Aggregation functions created using
-- AggregationFactory, convenient to transfer 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
)