This variable directs the interface to select key columns only when searching for records. Its use can improve READ performance on large tables with many rows.
When set to True (on, yes), the default value, A_MSSQL_SELECT_KEY_ONLY causes the interface to select only key columns when searching for records, and then select the entire row of the single record that must be returned to the COBOL program. This improves performance on large tables with many rows.
Setting A_MSSQL_SELECT_KEY_ONLY to False (off, no) does not affect how the select is created for files open I/O (since the record must be locked and then the rest of the data fetched), but causes the interface to select all the columns of the table for files open INPUT.