基本上，听起来您的EMSData表中没有匹配的数据。您需要为此使用外部联接：

Basically it sounds like you don't have matching data in your EMSData table. You would need to use an OUTER JOIN for this:

SELECT *
FROM csusaCIDPull
    LEFT JOIN CustomerData ON CustomerData.CustomerID = csCIDPull.CustomerID
    LEFT JOIN EMSData ON EMSData.EmsID = csCIDPull.EmsID

A SQL连接的视觉解释

侧面说明：考虑不返回 * 而是选择每个表格中您想要的字段。

Side note: consider not returning * but rather select the fields you want from each table.