Remove "*" column from aggregation results with COUNT(*)

[fupelaqu]

Description

When performing an aggregation with COUNT(*) or similar expressions using *, the result set includes a literal * column alongside the aggregation result. This column is meaningless in the context of an aggregation and should not be returned.

Example

SELECT COUNT(*) FROM ecommerce

Current result set:

*	COUNT(*)
	20

Expected Behaviour

Only the aggregated columns should be returned:

COUNT(*)
20

Impact

• The * column has no meaningful value in aggregation results
• Confuses downstream tools and users
• Breaks schema expectations in Arrow Flight SQL and JDBC clients that try to interpret the column
• Combined with issue Remove empty "bucket_root" column from aggregations without GROUP BY #42 (bucket_root), a simple COUNT(*) query returns 3 columns instead of 1

Notes

This is related to but distinct from issue #42. Both the bucket_root and * columns should be suppressed for clean aggregation output.