Reject zero-column table creation with AO column storage

[yjhjstz]

Creating a table with AO columnar storage and no columns is not supported. This patch adds an explicit check in DefineRelation() to throw an error when such a case is encountered. This ensures users receive a clear error message rather than encountering undefined behavior.

Also adds a regression test under misc_jiras to verify the behavior.

Fixes #1055

What does this PR do?

Type of Change

• Bug fix (non-breaking change)
• New feature (non-breaking change)
• Breaking change (fix or feature with breaking changes)
• Documentation update

Breaking Changes

Test Plan

• Unit tests added/updated
• Integration tests added/updated
• Passed make installcheck
• Passed make -C src/test installcheck-cbdb-parallel

Impact

Performance:

User-facing changes:

Dependencies:

Checklist

• Followed contribution guide
• Added/updated documentation
• Reviewed code for security implications
• Requested review from cloudberry committers

Additional Context

CI Skip Instructions

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[gfphoenix78]

I have two concerns about the issue:

1. What's the behavior if we drop the aocs table to zero column?
2. Is it possible to convert other type of table with zero column to aocs table?

[avamingli]

What's the behavior if we drop the aocs table to zero column?
Is it possible to convert other type of table with zero column to aocs table?

@gfphoenix78 can you provide sql ?

create a table with one column, then drop the column.

Same concern, create a table with zero column is valid in Postgres/GPDB.

[avamingli]

What's the behavior if we drop the aocs table to zero column?
Is it possible to convert other type of table with zero column to aocs table?

@gfphoenix78 can you provide sql ?

create a table with one column, then drop the column.

Same concern, create a table with zero column is valid in Postgres/GPDB.

What's the behavior if we drop the aocs table to zero column?
Is it possible to convert other type of table with zero column to aocs table?

@gfphoenix78 can you provide sql ?

create a table with one column, then drop the column.

Same concern, create a table with zero column is valid in Postgres/GPDB.

Designed to be valid.
https://www.postgresql.org/docs/14/sql-createtable.html

Zero-Column Tables
PostgreSQL allows a table of no columns to be created (for example, CREATE TABLE foo();). This is an extension from the SQL standard, which does not allow zero-column tables. Zero-column tables are not in themselves very useful, but disallowing them creates odd special cases for ALTER TABLE DROP COLUMN, so it seems cleaner to ignore this spec restriction.

[yjhjstz]

Is it possible to convert other type of table with zero column to aocs table?

fec6f10 try to reject , if agreed, then I will add related testcase.

[gfphoenix78]

What's the behavior if we drop the aocs table to zero column?
Is it possible to convert other type of table with zero column to aocs table?

@gfphoenix78 can you provide sql ?

create a table with one column, then drop the column.

Same concern, create a table with zero column is valid in Postgres/GPDB.

Yes. The normal table with columns may drop columns one by one, until to have no column.

This PR only disallow aocs table to create a zero-column table, but we may still have zero-column table in other table storage. ALTER TABLE ... SET ACCESS METHOD may convert other table storage to aocs, which is also invalid.

[gfphoenix78]

Please add more test cases here:

1. alter table ... drop column ... to drop columns one by one until to zero-column.
2. alter table ... set access method from other type of table storage to aocs.

[yjhjstz]

drop columns one by one until to zero-column

wild to reject drop column to zero ?