Database Reference
In-Depth Information
stance that executes when a new session (or instance) is given to a user when they log
in.
Execution
It's important to understand when a computation is executed relative to when a value is
shown on a page and to when other values are available to the computation. When us-
ing the value of an item in a computation, the current session state for that item is the
value that is used. A computation sets an item value in session state, and any process-
ing (computations, validations, or processes) that uses that item after it has been set
sees the results of that computation. When a page is rendered, it shows what is in the
session state for that item at the time it's shown on the page. The computation point is
the setting that determines when the computation is executed.
On the page definition screen, several computation points are shown in the page
tree. You can adjust the computation point by clicking and dragging the computation in
the tree to a different computation point, or by editing the computation and changing
the values for the sequence and computation point directly. The sequence only orders
the computations within a given computation point. In general, the page renders and
processes as shown on the page definition screen, starting at the top and going down
the list to the bottom. There are only minor exceptions, such as dynamic actions and
AJAX callbacks, which have variable points of execution.
Types
Computations have much of the same flexibility as other APEX components. They can
be complex or simple, with the full capabilities of the Oracle Database to support them.
The types of computations are as follows:
•
Static Assignment
: Simple static text value
•
PL/SQL Function Body
: PL/SQL function syntax with a
RETURN
statement
•
SQL Query (Return Single Value)
: Any SQL statement as long as it returns
a single row and a single column
•
SQL Query (Return Colon Separated Values)
: SQL used for multiselect
items
•
SQL Expression
: Expression used in the
SELECT
portion of an SQL state-
ment
