mysql - SQL 查询 - 提取带有空值的查询

Question

我目前正在通过 Azure 使用 API 连接到我的应用程序。我正在运行一个查询，该查询填充用户药物的 ListView 。用户可以选择是否在用药的同时添加诊断信息。如果用户添加药物和诊断，则查询成功并将填充数据库和 ListView 。但如果用户没有添加诊断，数据库会成功更新，userdiagnosis 字段为空，但不会显示在应用的 ListView 中。

有什么方法可以允许在查询中运行空值并仍然成功提取数据吗？

这是我当前的查询:

var api = {
// an example of executing a SQL statement directly
get: (request, response, next) => {
    var query = {
        sql: 'SELECT  dbo.usermedication.id, \
        dbo.medicine.id AS medicationid,  \
        dbo.medicine.medname, \
        dbo.usermedication.isactive, \
        dbo.usermedication.reminder, \
        dbo.usermedication.communityfeedback, \
        dbo.usermedication.frequency, \
        dbo.usermedication.directions, \
        dbo.medicine.dosage, \
        dbo.usermedication.datetimetotake,  \
        dbo.userdiagnosis.id as "userdiagnosisid", \
        dbo.diagnosis.id AS diagnosisid, \
        dbo.diagnosis.diagnosistext \
        FROM dbo.usermedication 
        INNER JOIN dbo.medicine ON dbo.usermedication.medicationid = dbo.medicine.id  
        INNER JOIN dbo.userdiagnosis ON dbo.usermedication.userdiagnosisid = dbo.userdiagnosis.id  
        INNER JOIN dbo.diagnosis ON dbo.userdiagnosis.diagnosisid = dbo.diagnosis.id 
        WHERE dbo.usermedication.userid = @userid AND dbo.usermedication.isactive = 1',
        parameters: [
            { name: 'userid', value: request.query.userid }
        ]
    };

    request.azureMobile.data.execute(query)
        .then(function (results) {
            response.json(results);
        });
}

};

module.exports = api;

Answer 1

据我从您给出的问题陈述中了解到，如果用户不添加诊断，则 dbo.diagnosis 表将不会有条目，但 dbo.usermedication 将成功更新。 由于您在这些表上使用了 INNER JOIN，显然该列表不会有，因为 dbo.diagnosis 表中没有匹配的记录。

如果您考虑在 dbo.diagnosis 上使用 LEFT JOIN，那么即使诊断表中的值为 null，您也将能够从 userMedicate 表中获取记录。

如果这是预期的话，请尝试一下。

也许你可以尝试运行如下所示的内容

WITH  (SELECT * FROM dbo.userdiagnosis  
    INNER JOIN dbo.diagnosis ON dbo.userdiagnosis.diagnosisid = dbo.diagnosis.id ) AS diagnosisDetails,
SELECT  dbo.usermedication.id, \
    dbo.medicine.id AS medicationid,  \
    dbo.medicine.medname, \
    dbo.usermedication.isactive, \
    dbo.usermedication.reminder, \
    dbo.usermedication.communityfeedback, \
    dbo.usermedication.frequency, \
    dbo.usermedication.directions, \
    dbo.medicine.dosage, \
    dbo.usermedication.datetimetotake,  \
    DiagnosisDetails.id as "userdiagnosisid", \
    DiagnosisDetails.diagnosistext \
    FROM dbo.usermedication 
    INNER JOIN dbo.medicine ON dbo.usermedication.medicationid = 
dbo.medicine.id  
    LEFT JOIN diagnosisDetails ON dbo.usermedication.userdiagnosisid = diagnosisDetails.id  
    WHERE dbo.usermedication.userid = @userid AND dbo.usermedication.isactive = 1;