Fabian Hueske created CALCITE-7732:
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Summary: Make the TABLE keyword optional for table function calls
in LATERAL context
Key: CALCITE-7732
URL: https://issues.apache.org/jira/browse/CALCITE-7732
Project: Calcite
Issue Type: Improvement
Components: core
Reporter: Fabian Hueske
h3. Summary
Calcite currently requires the {{TABLE}} keyword when a table function is
invoked together with the explicit {{LATERAL}} keyword. This issue proposes
making {{TABLE}} optional in that position, so that both of the following are
accepted:
{code:sql}
-- explicit form (still supported, unchanged)
SELECT * FROM t, LATERAL TABLE(fn(t.a))
-- new, TABLE keyword omitted
SELECT * FROM t, LATERAL fn(t.a)
{code}
The {{TABLE}} keyword remains fully supported, it simply becomes optional.
Existing queries continue to parse and behave exactly as before; this is a
purely additive, backward-compatible change.
h3. Motivation
As of CALCITE-6254 (1.37.0), a table function can be invoked in the
{{{}FROM{}}}/{{{}JOIN{}}} position without the {{TABLE(...)}} wrapper:
{code:sql}
SELECT * FROM fn(args) -- OK since 1.37.0
SELECT * FROM t JOIN fn(args) ON ...
{code}
However, once the {{LATERAL}} keyword is written explicitly, the {{TABLE}}
wrapper becomes mandatory again. This leaves an inconsistent matrix:
||Syntax||Supported today||
|{{FROM t, fn(args)}} (implicit lateral, no {{{}TABLE{}}})|(/) (CALCITE-6254)|
|{{FROM t, LATERAL TABLE(fn(args))}}|(/)|
|{{FROM t, TABLE(fn(args))}}|(/)|
|{{FROM t, LATERAL fn(args)}}|(x)|
Requiring {{TABLE}} _only_ when {{LATERAL}} is spelled out is a syntactic
inconsistency. The {{TABLE}} keyword adds no information in this context and
bloats the syntax. Several vendors treat it as optional. Making it optional
under {{LATERAL}} completes the matrix and aligns the two spellings.
h3. Backward compatibility
Fully backward compatible:
* {{TABLE}} stays a legal, supported keyword — it is only made optional.
* All existing queries ({{{}LATERAL TABLE(fn(...)){}}},
{{{}TABLE(fn(...)){}}}, plain {{{}fn(...){}}}) parse and behave identically.
* The change only adds an optional syntax path; no existing behavior is
removed or altered.
h3. References
* CALCITE-6254 — Support table function calls in FROM clause without TABLE()
wrapper (direct precedent, 1.37.0)
* CALCITE-1490 — Allow table functions without explicit TABLE (dup of 6254)
* CALCITE-4396 — Allow table valued functions in FROM and JOIN without TABLE
clause (dup of 6254)
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