Creating trigger to allow INSERT if existing data is not null - sql

Question

I have the following table and I want to create a trigger that allows the insertion of values if the value of 'ActualLeaveDate' is not null:
CREATE TABLE Bed
(
PatBedNum NUMBER GENERATED BY DEFAULT AS IDENTITY START WITH 1 INCREMENT BY 1,
WardNum NUMBER(4),
BedNum NUMBER(2),
PatNum VARCHAR2(6) CHECK (PatNum LIKE '%P%'),
DateOnWaitlist DATE,
ExpectedStayDuration VARCHAR2(8) CHECK (ExpectedStayDuration LIKE '% days%'),
DatePlacedInWard DATE,
ExpectedLeaveDate DATE,
ActualLeaveDate DATE,
CONSTRAINT BedPK PRIMARY KEY (PatBedNum),
CONSTRAINT PatBedNum FOREIGN KEY (PatNum)
REFERENCES Patient (PatNum) ON DELETE CASCADE,
CONSTRAINT PatWardNum FOREIGN KEY (WardNum)
REFERENCES Ward (WardNum) ON DELETE CASCADE
);
I tried to create a trigger using the following script:
CREATE TRIGGER BedCheck2
BEFORE INSERT ON BED
FOR EACH ROW
BEGIN
IF (:Old.ActualLeaveDate IS NOT NULL)
THEN
INSERT INTO Bed (PatBedNum, WardNum, BedNum, PatNum, DateOnWaitlist, ExpectedStayDuration, DatePlacedInWard, ExpectedLeaveDate, ActualLeaveDate)
VALUES (:New.PatBedNum, :New.WardNum, :New.BedNum, :New.PatNum, :New.DateOnWaitlist, :New.ExpectedStayDuration, :New.DatePlacedInWard, :New.ExpectedLeaveDate, :New.ActualLeaveDate);
ELSE
RAISE_APPLICATION_ERROR (-20002, 'Bed ' || :Old.BedNum || 'is not empty!');
END IF;
END;
/
However, when I enter the following insert command, it skips the insertion portion of the trigger:
INSERT INTO BED VALUES (5, 11, 84, 'P10787', '12/1/20', '5 days', '17/1/20', '22/1/20', NULL);
Additionally, it straights directly to the RAISE_APPLICATION_ERROR even though the data in 'ActualLeaveDate' in the database IS NOT NULL.
Am I missing something here or doing something wrong?

Answer 1

Why not simply add a NOT NULL constraint to that column?
CREATE TABLE Bed (
...,
ActualLeaveDate DATE NOT NULL,
...
)
If you want to prevent both ActualLeaveDate and BedNum to be null (or not null), you can use a check constraint:
CREATE TABLE Bed (
...,
BedNum NUMBER(2),
ActualLeaveDate DATE,
...
CHECK (
(BedNum IS NOT NULL AND ActualLeaveDate IS NULL)
OR (BedNum IS NULL AND ActualLeaveDate IS NOT NULL)
)
)