Q(uick)BASIC Statement: UPDATE

Quick View

UPDATE

A statement that adds an updated record to an ISAM table, overwriting the current record

Worth knowing

Useful and cross-version information about the programming environments of QBasic and QuickBasic.

Syntax

UPDATE [#]filenumber%,recordvariable

Description/Parameter(s)

filenumber%	The number of an open ISAM table.
recordvariable	A variable of the user-defined type tabletype that was specified in the OPEN statement.

The argument filenumber% is the number used in the OPEN statement to open the table.
The argument recordvariable is a variable of the user-defined type corresponding to the table. It is the record that will overwrite the current record.

Usage Notes

UPDATE replaces the current record with recordvariable. It remains the current record.
Use RETRIEVE to fetch the current record and place its data into recordvariable. You can change the data in recordvariable, then use the UPDATE statement to update the current record with the changes you've made.
Use INSERT to add a record to a table without overwriting the current record.
If the values passed to recordvariable do not match the record structure in the user-defined type, BASIC generates the error message, "Type mismatch." The record structure includes the names and types of columns or fields.
BASIC removes trailing spaces from strings used in an update.

Example

This example uses the CREATETABLE statement to create a new table in an ISAM file and uses the SEEK, RETRIEVE, UPDATE, and INSERT statements to insert records into it. It uses the LOF function to display the number of records in the new table and then destroys the table with DELETETABLE.
Note: To run this program, you must load the ISAM TSR program PROISAMD.EXE. Also, this program assumes a file called BOOKS.MDB exists in the current directory. BOOKS.MDB is a sample ISAM file that SETUP copies to your disk.
If this program is interrupted before the database is closed, the file BOOKS.MDB may be left in an inconsistent state.

DEFINT A-Z
TYPE BookRec
    IDNum AS DOUBLE             'Unique ID number for each book.
    Price AS CURRENCY           'Book's price.
    Edition AS INTEGER          'Book's Edition
    Title AS STRING * 50        'Book's title.
    Publisher AS STRING * 50    'Book's publisher.
    Author AS STRING * 36       'Book's author.
END TYPE
 
CONST Database = "BOOKS.MDB"    'Name of the disk file.
CONST tablename = "BookStock"   'Name of the table.
DIM Library AS BookRec          'Variable for current record.
DIM MinPrice AS CURRENCY        'SEEK criteria.
 
    CLS
    'Open existing table.
    LibraryFile = FREEFILE
    OPEN Database FOR ISAM BookRec tablename AS LibraryFile
    CREATEINDEX LibraryFile, "Library", 0, "Price"
    SETINDEX LibraryFile, "Library"
 
    'Create and open a new table.
    NewFile = FREEFILE
    OPEN Database FOR ISAM BookRec "PricyBooks" AS NewFile
 
    'Fill new table with records for all books with price >= MinPrice.
    DO
        DO
            INPUT "Display books that cost as much or more than "; MinPrice
            IF MinPrice < 0 THEN PRINT "Positive values only, please."
        LOOP UNTIL MinPrice >= 0
 
        SEEKGE LibraryFile, MinPrice
        IF EOF(LibraryFile) THEN
            PRINT "There are no books greater than"; MinPrice
        END IF
    LOOP WHILE EOF(LibraryFile)
 
    DO
        RETRIEVE LibraryFile, Library
        INSERT NewFile, Library
        MOVENEXT LibraryFile
    LOOP UNTIL EOF(LibraryFile)
 
    'Loop through new table twice: first time ask for price increase;
    'second time display new price.
    FOR count = 1 TO 2
        CLS
        PRINT SPC(18); "There are"; LOF(NewFile); "books that cost at least ";
        PRINT USING ("$###.##"); MinPrice
        PRINT " ID Number"; SPC(3); "Title"; SPC(20); "Author";
        PRINT SPC(11); "Publisher"; SPC(10); "Price"
        VIEW PRINT 3 TO 20
        MOVEFIRST NewFile
        DO
            RETRIEVE NewFile, Library
            PRINT Library.IDNum; " "; LEFT$(Library.Title, 20);
            IF LEN(RTRIM$(Library.Title)) > 20 THEN
                PRINT "...  ";
            ELSE
                PRINT "     ";
            END IF
            PRINT LEFT$(Library.Author, 15); "  ";
            PRINT LEFT$(Library.Publisher, 16); "  ";
            PRINT USING ("$###.##"); Library.Price
            MOVENEXT NewFile
        LOOP UNTIL EOF(NewFile)
 
        IF count = 1 THEN
            VIEW PRINT 20 TO 24: LOCATE 20, 1
            DO
                INPUT "Increase cost by how much (0-100%)"; increase
                IF increase < 0 OR increase > 100 THEN PRINT "Illegal value"
            LOOP UNTIL increase >= 0 AND increase <= 100
 
            'Update records in PricyBooks.
            MOVEFIRST NewFile
            DO
                RETRIEVE NewFile, Library
                Library.Price = (Library.Price * (100 + increase)) / 100
                'Overwrite record with increased price.
                UPDATE NewFile, Library
                'Force ISAM to flush the buffer to disk.
                CHECKPOINT
                MOVENEXT NewFile
            LOOP UNTIL EOF(NewFile)
        END IF
        VIEW PRINT 1 TO 19
    NEXT count
 
    'Destroy index and temporary table, close files.
    DELETEINDEX LibraryFile, "Library"
    CLOSE
    DELETETABLE Database, "PricyBooks"
    END