Constant DISCOVER_PRIMARY_KEY_QUERY 

const DISCOVER_PRIMARY_KEY_QUERY: &str = r#"
    SELECT a.attname as column_name
    FROM pg_index i
    JOIN pg_class c ON c.oid = i.indrelid
    JOIN pg_namespace n ON n.oid = c.relnamespace
    JOIN pg_attribute a ON a.attrelid = i.indrelid AND a.attnum = ANY(i.indkey)
    WHERE n.nspname = $1
      AND c.relname = $2
      AND i.indisprimary = true
    ORDER BY array_position(i.indkey, a.attnum)
"#;

SQL query to discover primary key columns directly from PostgreSQL system tables. This bypasses querying information_schema.table_constraints to avoid permission issues. Match pg_class and pg_namespace by exact catalog names instead of casting a constructed string to regclass, as unquoted regclass input folds mixed-case table names to lower case.