sql - SQLITE3子查询

Question

我有一个问题，即使在这里和sqlite.org重新注册后，我也无法解决

所以，我有这些表：

CREATE TABLE MEDICO(
    idMedico INTEGER PRIMARY KEY AUTOINCREMENT,
    nome VARCHAR(50) NOT NULL,
    morada VARCHAR(50) NOT NULL,
    telefone VARCHAR(9) NOT NULL
);



CREATE TABLE PRESCRICAO(
    idPrescricao INTEGER PRIMARY KEY AUTOINCREMENT,
    idConsulta INTEGER,
    idMedico INTEGER NOT NULL,
    nrOperacional INTEGER NOT NULL,
    FOREIGN KEY(idConsulta) REFERENCES CONSULTA(idConsulta),
    FOREIGN KEY(idMedico) REFERENCES MEDICO(idMedico),
    FOREIGN KEY(nrOperacional) REFERENCES UTENTE(nrOperacional)
);


CREATE TABLE PRESCRICAO_MEDICAMENTO(
    idPrescricao INTEGER ,
    idMedicamento INTEGER,
    nrEmbalagens INTEGER NOT NULL,
    FOREIGN KEY(idPrescricao) REFERENCES PRESCRICAO(idPrescricao),
    FOREIGN KEY(idMedicamento) REFERENCES MEDICAMENTO(idMedicamento),
    PRIMARY key(idPrescricao, idMedicamento)
);

我想要MEDICO最常用的idMedicamento可以说idMedico = 7，
直到这里，一切都很好，我正在做：

  SELECT idmedicamento, MAX(total) as maximum
    FROM (SELECT idMedicamento, COUNT(idMedicamento) AS total
        FROM PRESCRICAO_MEDICAMENTO
        WHERE PRESCRICAO_MEDICAMENTO.idPrescricao IN (
            SELECT idPrescricao FROM PRESCRICAO
            WHERE PRESCRICAO.idmedico= 7
        )
        GROUP BY idMedicamento);

我得到：

IDmedicamento：3
最多：5

这是我想要的，这是正确的。

但是当我这样做时：

SELECT idMedicamento
FROM (SELECT idMedicamento, MAX(total) as maximum
FROM (SELECT idMedicamento, COUNT(idMedicamento) AS total
    FROM PRESCRICAO_MEDICAMENTO
    WHERE PRESCRICAO_MEDICAMENTO.idPrescricao IN (
        SELECT idPrescricao FROM PRESCRICAO
        WHERE PRESCRICAO.idmedico= 7
    )
    GROUP BY idMedicamento));

我所得到的是MEDICO最后使用的idMedicamento，在这种情况下，是idMedicamento = 5的MEDICAMENTO。

知道我在做什么错吗？真的无法弄清楚。

谢谢

Answer 1

在许多情况下，从记录中获取最大值的其他列的最简单方法是使用ORDER BY / LIMIT 1：

SELECT idMedicamento
FROM PRESCRICAO_MEDICAMENTO
WHERE idPrescricao IN (SELECT idPrescricao
                       FROM PRESCRICAO
                       WHERE idmedico = 7)
GROUP BY idMedicamento
ORDER BY COUNT(*) DESC
LIMIT 1