Searching a database

One of the most important uses of a database system is to allow the user to retrieve from a database those records that meet certain criteria. For example, one may wish to retrieve the records of all the persons who live in the London postal area. In dLabel terms this is Searching the database. More precisely, it is probably searching the address field of records in the database to find those that contain the word London.

Searches are carried out by selecting the Search and Mark item of the Records menu, entering the appropriate search text, and then pushing the Mark button. The number of records “marked” (ie found during the search) is displayed in the dialog.

Exiting the dialog by pushing the OK button causes dLabel to display only the marked records. (Return to normal display by unchecking the Show Marked Only item on the View menu).

But dLabel can do more than this. Suppose you wish to retrieve the records of those persons who live in London and are aged over 65. dLabel can do this by first searching the address field of records in the database to find those which contain the word London, and then narrowing the search to include only those records so far retrieved which contain a year of less than 1932 in the year of birth field.

You may then decide to widen the search to include the records of anyone who lives in York, or to exclude from the search any records of persons without a telephone. dLabel can do all of these things.

So to the concept of searching a database for records which meet one specific criterion we may add the concepts of narrowing a search so that only records already found AND which meet a new criterion are included. Similarly widening a search so that records already found OR any which meet a new criterion may be undertaken, and records may be excluded from a previous search.

When you carry out a search of a database with dLabel, dLabel will "mark" the records in the database which meet the criteria you specify. dLabel will then display on screen only those records which have been marked. If you wish, dLabel will print out the records that have been marked. You can even mark or unmark records manually if you wish to modify the list of those found by automatic searching.

Command line parameters