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A self-referencing alert compares the value of a date and time column with the value of an implicit input called :DATE_LAST_CHECKED in the WHERE clause of the alert Select statement. An implicit input is an input that Oracle Alert automatically provides the value for. When checking a self-referencing alert, Oracle Alert automatically provides the date and time as the value for :DATE_LAST_CHECKED.
When Oracle Alert checks your alert, it uses the date and time information in the column you specify in your Where clause to determine whether the exceptions returned by the alert Select statement were created or updated since the date the alert was last checked. Your self-referencing alert returns only those exceptions that occurred more recently than the date and time value of :DATE_LAST_CHECKED. Then, Oracle Alert updates the value of :DATE_LAST_CHECKED with the date and time information from the current alert check. See: How Oracle Alert Checks Alerts.
Oracle Alert never displays :DATE_LAST_CHECKED in the Inputs alternative region of either the Alert Details window or the Action Sets window in the Alerts form.
. . WHERE ... AND TO_DATE(creation_date, 'DD-MON-YYYY HH24:MI:SS') > TO_DATE(:DATE_LAST_CHECKED, 'DD-MON-YYYY HH24:MI:SS')
Attention: The format of the date and time information in the column in the Where clause must match the format of the date and time information in :DATE_LAST_CHECKED. The format of the date and time information stored in the DATE_LAST_CHECKED column is:
DD-MON-YYYY HH24:MI:SS
Attention: If you choose to use the TO_DATE function to modify date and time information, you must use it to modify both the column your alert references and the DATE_LAST_CHECKED column.
Creating an Action Set for an Alert
Overview of Oracle Alert History
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