List schemas the connected read-only role can access.

List tables and views in schema with an estimated row count and comment.

Returns columns=[name, row_estimate, comment, kind]. row_estimate comes from the planner statistics (pg_class.reltuples) and is approximate; it is null for views.

Describe a table: columns, types, nullability, primary key, FKs, indexes.

Columns come back flat as column_names (the field labels) and column_rows (one positional row per column), in ordinal position.

Return the first n rows of a table. n is clamped to 1..50.

Run a single read-only SELECT and return a bounded, columnar result.

Accepts one statement of any read-only shape: SELECT, WITH ... SELECT, UNION / UNION ALL / INTERSECT / EXCEPT, and any nesting of those. Rejected before execution: multiple statements, DML/DDL anywhere in the tree (including data-modifying CTEs), SELECT ... INTO, COPY, row locking, and any function not on the read-only allowlist (pg_read_file, dblink, ...).

The query is wrapped in SELECT * FROM (<sql>) sub LIMIT max_rows, so the cap applies to the combined result of a set operation, not to one branch. max_rows defaults to 100 and is capped at 1000. The response is separately capped in bytes, in which case truncated is true.

Performance note: plain UNION deduplicates, which costs a sort or hash over the full result of both branches before any row is returned — the outer LIMIT cannot short-circuit it. On large tables that is the most likely way to hit the server's statement timeout. Prefer UNION ALL when you do not need duplicates removed.