Improve an access method

The super_access access method in the example has no purpose functions to open or close files or smart large objects. The get_next_record() function must open and close any data and keep an indicator that notifies get_next_record() to open only at the start of the scan and close only after it completes the scan.

The incomplete super_access access method example does not create a virtual table because the example does not include an am_create purpose function or add, delete, or update rows.

To enable INSERT, DELETE, and UPDATE statements to execute, the access method must provide registered UDRs for the am_open, am_close, am_insert, am_delete, and am_update purpose functions.