Question

I have 2 tables, Organisation and State(where it is). Each Organisation has a state. I would now like to implement a Integer column for the table State which keeps tracks of how many organisations are in it. Kinda like whenever a new organisation is inserted into Organisations table, update integer column in corresponding State table where org.state_id = state_id.

Is this possible using triggers?

Answer 1

I agree with Glenn’s answer that, all things being equal, on-demand is a better solution, but the answer is that, yes, it can be done with a trigger. Very easily.

CREATE TRIGGER organization_trigger_insert AFTER INSERT ON organization
    FOR EACH ROW BEGIN
        UPDATE state SET total = total + 1 WHERE NEW.state_id = state_id;
    END;

CREATE TRIGGER organization_trigger_delete BEFORE DELETE ON organization
    FOR EACH ROW BEGIN
        UPDATE state SET total = total - 1 WHERE OLD.state_id = state_id;
    END;

Demo