MySQL:indsæt hvor ikke eksisterer

Brug insert . . . select :

INSERT INTO USER (name, email)
    SELECT 'John', 'example@sqldat.com'
    WHERE NOT EXISTS
        (SELECT id FROM USER WHERE email = 'example@sqldat.com');

Jeg ville skrive dette som:

INSERT INTO USER (name, email)
    SELECT name, email
    FROM (SELECT 'John' as name, 'example@sqldat.com' as email) t
    WHERE NOT EXISTS (SELECT 1 FROM USER u WHERE u.email = t.email);

Men en bedre tilgang er nok bare at indsætte et unikt indeks, så databasen beskytter dataene:

create unique index idx_users_email on user(email);