getPrimaryKeys( catalog, schema, table )
Gets a description of a table's primary key columns. They are ordered by COLUMN_NAME.
Each primary key column description has the following columns:
getPrimaryKeys( string catalog, string schema, string table )
If catalog is "" (the empty string), only procedures without a catalog are returned.
If catalog is the null value, catalog names are not part of the selection criteria.
If schema is "" (the empty string), only procedures without a schema are returned.