Oracle Trigger Syntax Using Subquery - sql

Question

I'm trying to write a Trigger in Oracle Syntax which, upon entering a line into a particular table, checks that both values entered belong to some classification that is held in another table. My initial thought was to have a constraint on the table that included a subquery but Oracle doesn't seem to like that.
The select query I have written in the below works - but I'm not sure how to put it into a trigger - but essentially I need the trigger to ensure that EW1.OrgId and EW2.OrgId are the same. Any help is appreciated!
CREATE TABLE Organisation (
OrgId INTEGER PRIMARY KEY,
Name VARCHAR(40) NOT NULL
);
CREATE TABLE Person (
PersonId INTEGER PRIMARY KEY,
FirstName VARCHAR(45) NOT NULL,
LastName VARCHAR(45) NOT NULL
);
CREATE TABLE Employee (
PersonId INTEGER PRIMARY KEY REFERENCES PERSON (PersonId) ON DELETE CASCADE
);
CREATE TABLE Manager (
PersonId INTEGER PRIMARY KEY REFERENCES PERSON (PersonId) ON DELETE CASCADE
);
CREATE TABLE EnlistedWith (
OrgId INTEGER REFERENCES ORGANISATION (OrgId) ON DELETE CASCADE,
PersonId INTEGER REFERENCES PERSON (PersonId) ON DELETE CASCADE,
PRIMARY KEY(OrgId,PersonId)
);
CREATE TABLE SupervisedBy (
EmployeeId INTEGER REFERENCES Employee (PersonId) ON DELETE CASCADE,
ManagerId INTEGER REFERENCES Manager (PersonId) ON DELETE CASCADE,
CONSTRAINT PK_SupervisedBy PRIMARY KEY (EmployeeId, ManagerId)
);
CREATE TRIGGER SupervisorCompany
AFTER INSERT ON SupervisedBy
FOR EACH ROW
BEGIN
declare qty INTEGER := 0;
BEGIN
SELECT COUNT (*) into qty
FROM SupervisedBy SB
INNER JOIN EnlistedWith EW1 ON SB.ManagerId = EW1.PersonId
INNER JOIN EnlistedWith EW2 ON SB.EmployeeId = EW2.PersonId
and EW1.OrgId <> EW2.OrgId
IF qty <> 0
then Raise_Error (1234567, 'Manager and Employee are not Enlisted with same Organisation');
END IF;
END;
END;

Answer 1

You can refer to the columns of the owner of a Trigger using :NEW / :OLD. So, your Trigger could be re-written as
CREATE OR REPLACE TRIGGER supervisorcompany AFTER
INSERT
ON supervisedby FOR EACH ROW
DECLARE qty INTEGER := 0;
BEGIN
SELECT count (*)
INTO qty
FROM enlistedwith ew1
WHERE ew1.personid = :NEW.managerid
AND EXISTS
(
SELECT 1
FROM enlistedwith ew2
WHERE ew2.personid = :NEW.employeeid
AND ew1.orgid <> ew2.orgid ) ;
IF qty <> 0 THEN
raise_application_error (1234567, 'Manager and Employee are not Enlisted with same Organisation');
END IF;
END;
/

Answer 2

There's some guessing involved... Maybe something like this
CREATE TRIGGER SupervisorCompany
AFTER INSERT
ON SupervisedBy
FOR EACH ROW
BEGIN
IF (SELECT OrgId
FROM EnlistedWith
WHERE PersonId = New.ManagerId)
<>
(SELECT OrgId
FROM EnlistedWith
WHERE PersonId = New.EmployeeId) THEN
RAISE_ERROR(1234567, 'Manager and Employee are not Enlisted with same Organisation');
END IF;
END;
is what you want? It checks if the OrgId of the row where the PersonId equals the newly entered ManagerId is the same as the one for the newly entered EmployeeId. If not, your error is raised.
(Untested, as no DDL for the tables were provided.)