Delete/Modify row in one table based on a condition

constraintforeign keyoracle

I have a table structure like

 create table EMPLOYE (
    CodeEmploye varchar2(100) not null,
    NAS varchar2(100),
    CONSTRAINT employe_pk primary key (CodeEmploye)
);

create table SALAIRE (
    CodeEmploye varchar2(100) not null,
    Mois number not null,
    CONSTRAINT salaire_pk primary key (CodeEmploye, Mois),
    CONSTRAINT salaire_code_employe_fk FOREIGN KEY(CodeEmploye) REFERENCES EMPLOYE(CodeEmploye)
);

I want to add a constraint where I should not be allowed to modify/delete a row in EMPLOYE table if the same employee exist in SALAIRE table.

What is the best way to do that ?

Best Answer

Prevent Delete

Add "on delete set null" to the FK constraint. Since the column is NOT NULL, this process can't happen.

 CONSTRAINT salaire_code_employe_fk FOREIGN KEY(CodeEmploye)
    REFERENCES EMPLOYE(CodeEmploye)
    ON DELETE SET NULL

Prevent Modify

What you'll need to do is check for "can you update?" during the UPDATE process. (eg within a trigger)

One method would look something like:

declare
  type CodeEmploye_nt_t is table of SALAIRE.CodeEmploye%type;

  CodeEmploye_nt   CodeEmploye_nt_t;
begin
  select a.CodeEmploye
    bulk collect into CodeEmploye_nt
  from SALAIRE a
  where a.CodeEmploye in ( new.CodeEmploye, old.CodeEmploye )
  FOR UPDATE; -- prevent other from modifying important SALAIRE rows
              -- while you're in the middle of a transaction

  raise some_error;
exception
  when no_data_found then
    null;
end;

Related Solutions

Mysql – “Cannot add or update a child row” when deleting a record

On the face of it, that does seem impossible.

The thing is, your error suggests it's not that you're trying to delete at all.

The message you're getting suggests you're trying to insert or update a row in the child table, not delete a row from the parent table. If the foreign key you posted was causing the problem relative to a delete, you should see this message, instead:

Cannot delete or update a parent row: a foreign key constraint fails (`test`.`bar`, CONSTRAINT `bar_ibfk_1` FOREIGN KEY (`foo_id`) REFERENCES `foo` (`id`))

It's also possible you have some BEFORE DELETE trigger magic on survey_main that's doing something unexpected.

Right after this error occurs, try this:

SHOW ENGINE INNODB STATUS;

The LATEST FOREIGN KEY ERROR section should give you something more to go on. Failing that, you could enable the general log, which will show queries executed by triggers and other stored programs, as well as the queries you're directly executing, to shed light on what might be going on behind the scenes.

Update (#1) Things are definitely not as they seem and the full table definitions are going to be pretty critical, here.

Also, the version of MySQL you're using may also be relevant, so please mention it.

With nothing more to go on at the moment, I'm speculating that you have invalid data in the survey_id column of the survey_answers table. To test that theory:

SELECT *
  FROM survey_answers sa
  LEFT JOIN survey_main sm ON sm.id = sa.survey_id
 WHERE sm.id IS NULL;

If I understand your schema correctly, then this query will return zero rows if I am wrong. :) If you get rows returned, then those rows have survey_answers records that contain an survey_id value that doesn't exist in the id column of survey_main.

Mysql – How to insert data into tables which reference each other?(MySQL)

Not sure I understood the task, but here is some food for thought for an alternative schema:

CREATE TABLE Departament(
    DepartamentID varchar(25) not null,
    Floor varchar(25) not null,
        CONSTRAINT pk_dept PRIMARY KEY (DepartamentID, Floor),
) ENGINE=InnoDB;


CREATE TABLE Employee(
    ID varchar(25) not null,
    DepartamentID varchar(25),
    Floor varchar(25),
        CONSTRAINT pk_ID PRIMARY KEY (ID),
        CONSTRAINT fk_dept FOREIGN KEY (DepartamentID, Floor) 
            REFERENCES Departament (DepartamentID, Floor)
) ENGINE=InnoDB;

CREATE TABLE Attendant (
    ID varchar(25) not null,
    DepartamentID varchar(25) not null,
    Floor varchar(25) not null,

    CONSTRAINT pk_attendent PRIMARY KEY (ID),
    CONSTRAINT ak_attendent UNIQUE (DepartamentID, Floor),
    CONSTRAINT fk_... REFERENCES Employee ...,
    CONSTRAINT fk_... REFERENCES Department ...,
) ENGINE=InnoDB;