How to check number of rows consistency in PostgreSQL?

Question

I have a database for saving various forms. I have a table of forms:

CREATE SEQUENCE seq_formtype;

CREATE TABLE formtype (
    id_ft integer NOT NULL DEFAULT nextval('seq_formtype'),
    name text
);

I have a table of different input fields in the form:

CREATE SEQUENCE seq_formstruct;

CREATE TABLE formstruct (
    id_fs integer NOT NULL DEFAULT nextval('seq_formstruct'),
    id_ft integer NOT NULL,
    name text,
    id_fstype text NOT NULL
);

And finally, I have a table in which I store the results from the form for each trial.

CREATE TABLE results (
    id_trial integer NOT NULL,
    id_fs integer NOT NULL,
    res_value text
);

When I add the result, I want to check whether all inputs from formstruct were inserted - that means that there will be for each entry in formstruct where formtype = typ_trialu (pseudocode) an entry in results.

Now I am not even sure how to check it or where to start. My idea was to create a trigger that would check the consistency after insertion to results (ie after insertion of all inputfield results).

Answer 1

It could be done with trigger(s) after insert statements.

CREATE TRIGGER check_form_types_trigger
    AFTER INSERT ON results
    FOR EACH STATEMENT
    EXECUTE PROCEDURE check_form_types_function();

And, in check_form_types_function (which should be plpgsql) you can raise an exception if your data (as a whole) are not consistent.

But, in the other hand, if you do this, you literally won't be able to insert partial data into results; you will be able to insert only whole data, with a single insert statement. And if you really care about consistency, you should do this check after each update & delete statements too.

Notes:

• names like fs, ft, fstype are terrible, consider rename your columns.
• consider using SERIALs (instead of just manually set up sequences)
• consider using foreign keys