Pathmaker Programming Guide

Reading Rows
How to Operate a DB Requester Application
B–2 067868 Tandem Computers Incorporated
READ FIRST (F4) If the end user wants to retrieve the first row (or rows) in the table ordered by a
selected key column, a READ FIRST operation is requested. When the end user
positions the cursor in a primary key column and presses F4, the first row that is
actually stored in the table is retrieved regardless of the value currently in the primary
key column on the screen. If an index column is selected, the first row in the table
sorted by the index column will be retrieved regardless of the value currently on the
screen.
(If duplicate index values exist when the READ FIRST operation is requested, the
application will return a row with the requested index value and the lowest primary
key value.)
READ FIRST Operation for an Outermost Box
A READ FIRST operation for an outermost box can be requested at any time by
pressing F4.
READ FIRST Operation for a Nested Box
To request a READ FIRST operation for a nested box, the end user must do the
following:
1. Initiate either a read or insert operation for the parent box.
2. Position the cursor in the nested box and press F4.
READ NEXT (F5) If a position has been established within a table by previously requesting another read
operation, the next row(s) can be retrieved in sequence by requesting a READ NEXT
operation. Suppose that a READ FIRST by primary key has been requested and that
the key value of the first row in the table is 100. The position within the table is at that
row. If the end user now requests a READ NEXT operation, the application will read
the next row with a primary key value greater than 100.
If an intervening insert, delete, or update operation is requested, the position within
the table is not lost. The READ NEXT operation can be continued as if the intervening
operation had not occurred.
After a function key for a read operation is pressed, the application displays a message
on the screen that identifies the key that the application will use if a READ NEXT
operation is requested.
READ NEXT Operation for an Outermost Box
If a READ FIRST has just been performed by primary key or index, the entire table can
be read by requesting repeated READ NEXT operations. To request a READ NEXT
operation, the end user must press F5.
READ NEXT Operation for a Nested Box
After a read operation on a nested box has been requested, repeated READ NEXT
operations can then be requested. To request a READ NEXT operation, the end user
must press F5.