Language reference

:= and query (views and result queries)

Syntax

<Name> := { <relational expression> };       -- define a named view
query { <relational expression> };            -- an anonymous result query
query <Name>;                                 -- emit a named view as a result

CustomerTotals := { γ customer_id, SUM(amount) → total (Orders) };
query { π customer_id, total (CustomerTotals) };

Description

The := assignment names an intermediate result (a "view") so you can build a query up in readable steps and reuse a sub-result by name. A query statement marks what the script should actually produce — either an inline expression or a previously-named view. Together they let you write a pipeline as a series of named stages ending in one or more results.

Technical Description

Name := { body } binds a QueryRelationSymbol whose body() is a RelNode; it is a logical view, inlined by the optimizer/planner at use sites (INLINE-001) so pushdown crosses former view boundaries. query { expr } registers a root query (an ExpressionQueryTarget, auto-named query[n]); query Name; registers a NamedQueryTarget. The SemanticModel's rootQueries drive execution, optimisation, and IR generation.

Examples

Build in stages and query the last:

OrderAmounts := { π order_id, amount (Orders) };
CustomerTotals := { γ customer_id, SUM(amount) → total (Orders) };
query CustomerTotals;

OrderAmounts := { PROJECT order_id, amount (Orders) };
CustomerTotals := { GROUP customer_id, SUM(amount) -> total (Orders) };
query CustomerTotals;

Anonymous inline result:

query { λ 10 (τ amount DESC (Orders)) };

query { LIMIT 10 (SORT amount DESC (Orders)) };

Reuse a view in two places:

Active := { σ active = true (Customers) };
query { Active ⋈ Orders };

Active := { SELECT active = true (Customers) };
query { Active JOIN Orders };

Limitations

A view is a logical definition, not a materialised table — it is recomputed (inlined) wherever used. A script with no query statement produces no output.

Outside a view, its columns answer to the view's name, not to the relations inside it. When the view reads a schema-on-read source (JSON, HTTP, MongoDB), a reference that still uses an inner relation's name is not refused. It yields NULL instead; see theta-join for a worked case.

Alternatives

A table-valued function (def … : RELATION) is a view that takes parameters.

Notes

Views are inlined before optimisation, so splitting a query into named views costs nothing at runtime and aids readability.