MySQL:जहां मौजूद नहीं है वहां डालें

insert . . . select :

INSERT INTO USER (name, email)
    SELECT 'John', '[email protected]'
    WHERE NOT EXISTS
        (SELECT id FROM USER WHERE email = '[email protected]');

मैं इसे इस प्रकार लिखूंगा:

INSERT INTO USER (name, email)
    SELECT name, email
    FROM (SELECT 'John' as name, '[email protected]' as email) t
    WHERE NOT EXISTS (SELECT 1 FROM USER u WHERE u.email = t.email);

लेकिन एक बेहतर तरीका यह है कि केवल एक अद्वितीय अनुक्रमणिका डालें ताकि डेटाबेस डेटा की सुरक्षा कर सके:

create unique index idx_users_email on user(email);