MySQL Join Where关联不存在

Question

我为在 2011 年有约会的网站的客户获取客户 ID

SELECT customers.id
FROM customers 
INNER JOIN sites ON customers.id = sites.customer_id
INNER JOIN appointments ON appointments.site_id = sites.id
WHERE YEAR(appointments.day) = 2011   

我正在寻找在 2011 年没有任何约会的客户。对如何去做感到困惑。

Answer 1

几种方式:

SELECT
    C.id
FROM
    Customers C
WHERE
    NOT EXISTS (
        SELECT *
        FROM
            Sites S
        INNER JOIN Appointments A ON
            A.site_id = S.id AND
            YEAR(A.day) = 2011
        WHERE
            S.customer_id = C.id
    )

或:

SELECT DISTINCT
    C.id
FROM
    Customers C
INNER JOIN Sites S ON
    S.customer_id = C.id
LEFT OUTER JOIN Appointments A ON
    A.site_id = S.id AND
    YEAR(A.day) = 2011
WHERE
    A.id IS NULL