[justint-db]

Summary

• Reserve AGG. Ossie SQL reserves the function name AGG for evaluating a measure, as defined by the Relational Query Interface (Sections 4 and 6). Implementations and dialect extensions must not give it another meaning. This change reserves the name only. Where model declarations may use AGG is left to a future version (docs(core-spec): Let dataset-scoped metrics reference source columns as source.column #633 proposes one use).
• Compatibility note. Earlier versions did not reserve AGG, so an older OSSIE_SQL_2026 expression might call a different function by that name. Fields, metrics, and columns can still be named agg.
• Function names should be case insensitive, matching the existing rule for regular identifiers. As suggested on the list, this is stated as a general rule, so it also covers existing functions.

Only core-spec/expression_language.md changes.

Related Issues

Split from #633.

Checklist

Specification

• Spec changes are included in core-spec/ and follow the existing structure
• Spec changes have been discussed on the mailing list or in a linked issue
• Breaking changes to the spec are clearly called out in the summary (see the compatibility note)

[jbonofre]

Thanks @justint-db, this matches what we agreed on the dev@ mailing list (split from #633 ):

• AGG is reserved in Ossie SQL, with a compatibility note for existing expressions calling another function named AGG
• function names are case insensitive, so agg() and Agg() are covered too
• function names and identifiers are separate namespaces, so a field or metric named agg still works
• where model declarations can use AGG (dataset scoped metric, AGG over a source measure) stays in #633

A few non-blocking points we can address later:

1. The compatibility note suggests moving an older AGG call to a vendor dialect, but the new section says a dialect extension MUST NOT define AGG. As vendor dialects are opaque (spec.md), I think the reservation should apply to OSSIE_SQL_2026 expression only.
2. It would be good to say explicitly that AGG(...) is not allowed in OSSIE_SQL_2026 model expressions until a future version defines where it can be used (maybe in the "Not Supported in Expressions" table).
3. Functions callable without parentheses (CURRENT_DATE, CURRENT_TIME, CURRENT_TIMESTAMP) can collide with a field of the same name. Worth an exception in the "separate namespaces" sentence.