fix(postgres): scope describeTable enum lookup to the column's schema - #18388

Pull Request check-list

• Have you added new tests to prevent regressions?
• If a documentation update is necessary, have you opened a PR to the documentation repository?
• Did you update the typescript typings accordingly (if applicable)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
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Description of change

describeTableQuery's "special" subquery resolves enum labels by pg_type.typname with no namespace filter:

(SELECT array_agg(e.enumlabel)
 FROM pg_catalog.pg_type t
 JOIN pg_catalog.pg_enum e ON t.oid = e.enumtypid
 WHERE t.typname = c.udt_name) AS "special"

Enum types are named enum_<table>_<column> and created in the table's schema, so two schemas holding a table of the same name end up with a same-named enum type in each, and the subquery matches both.

array_agg keeps the result to one row, so unlike the sibling "Comment" subquery this doesn't raise an error and instead silently concatenates the labels of every same-named enum. On a two-schema fixture, describeTable() reports this for a column declared ENUM('one', 'two'):

['one', 'two', 'three', 'four', 'five']

Joining pg_namespace and correlating on c.udt_schema returns only the labels of the type the column actually uses.

Verified against PostgreSQL 17.5: the added integration test fails on main with the merged array above and passes with the fix.

Relationship to #17511 / #18379

This is the independent of the bug in #17511 (for #18379), but has the same issue.

I have kept them in separate PRs because #17511 is already approved pending its test (which I have pushed to that branch).

This PR touches the next line in the same assertions in the describe-table-query.test.ts.

There is no issue filed for it; it was found while investigating #18379.

Summary by CodeRabbit

• Bug Fixes
  • Fixed PostgreSQL table descriptions to report enum values from the correct schema when identical enum or table names exist across schemas.
  • Prevented enum values from being incorrectly combined between schemas during table metadata inspection.
  • Preserved the declared order of PostgreSQL enum values in table descriptions.
  • Improved the accuracy and consistency of PostgreSQL table metadata for tables and enum types across multiple schemas.