sql - SQL具有计数和联接

我尝试过以下查询:在不到2家医院工作的医生是什么？但是结果不是我所期望的。

我有这些表:

CREATE TABLE Hospital (
    hid INT PRIMARY KEY,
    name VARCHAR(127) UNIQUE,
    country VARCHAR(127),
    area INT
);
CREATE TABLE Doctor (
    ic INT PRIMARY KEY,
    name VARCHAR(127),
    date_of_birth INT,
);
CREATE TABLE Work (
    hid INT,
    ic INT,
    since INT,
    FOREIGN KEY (hid) REFERENCES Hospital (hid),
    FOREIGN KEY (ic) REFERENCES Doctor (ic),
    PRIMARY KEY (hid,ic)
);

我尝试了这个:

SELECT DISTINCT D.ic
    FROM Doctor D, Work W
    JOIN Hospital H ON (H.hid = W.hid)
    WHERE D.bi = W.bi
    GROUP BY (D.ic)
    HAVING COUNT(H.hid) < 2
;

谢谢。

最佳答案

您需要使用LEFT JOIN，而不必与表Hospital联接

SELECT  a.name
FROM    Doctor a
        LEFT JOIN `Work` b
            ON a.ic = b.ic
GROUP BY a.name
HAVING COUNT(b.ic) < 2

关于sql - SQL具有计数和联接，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/13540563/