4. Extracting & updating data

A simple spreadsheet flat file database might make use of the Autofilter function to select certain records. And also the sort function could re-arrange the data.

If a record needs to added then the Insert Row function is used.

Extracting data

But for more complicated extractions a proper DBMS comes into its own. For example a database might contain sales from various departments over time. It is a simple matter for a DBMS to extract records according to a complicated set of conditions.

A language called SQL has been designed to cope with these complicated queries.

Inserting / changing data

A flat file can only be changed by one person at a time. Usually the first person to open the file has read-write access then anyone else has read-only access.

This is no good for a busy database.

A DBMS allows many records to be changed at the same time by different people. Sophisticated 'record-locking' ensures that changes do not interfere with one another.

For example if one person is changing a record, then that particular record is 'locked' from anyone else also trying to change it. Once the record is updated, it is released once more. Meanwhile there could be dozens \ hundreds of people changing unrelated records within the database at the same time.

For example a large travel agency would be constantly changing independent records.