Summary

Relax the projection parser to support standard grouped-aggregate SQL forms such as:

SELECT g1, g2, agg(v)
FROM t
GROUP BY g1, g2

Previously, the parser required projection.len() == 1, causing these queries to fall through to destination=none_unsupported.

Changes

• Walk the full projection list instead of requiring a single projection item

• Allow:

  • exactly one aggregate function
  • any number of plain column references

• Require every non-aggregate identifier in SELECT to also appear in GROUP BY, matching standard SQL semantics

This prevents cases like:

SELECT srcip, SUM(v)
FROM t
GROUP BY proto

from being silently interpreted as if srcip were never requested.

Still Unsupported

The parser continues to reject:

• multiple aggregates
• computed expressions
• literals
• wildcards (*)

The structural pattern model still supports only a single aggregate statistic.

Tests Added

Added 8 parser tests covering:

• group columns followed by aggregate

• aggregate-first ordering

• ClickHouse parametric quantile in multi-projection form

• structural equivalence between single- and multi-projection queries

• SELECT subset of GROUP BY

• rejection of:

  • non-GROUP BY identifiers
  • multiple aggregates
  • arbitrary expressions