将您的COUNT行切换为:

Switch your COUNT line to:

COUNT(DISTINCT OrderItems.kf_OrderID) AS `Line Item`

添加行时

INNER JOIN OrderItemComponents 
  ON OrderItemComponents.kf_OrderID = Orders.kp_OrderID

您返回了更多的行，因为我假设OrderItem可以包含多个组件.

you returned many more rows since an OrderItem can, I assume, contain multiple components.

更新

如果您有COUNT条语句，请尝试就地使用它:

Try using this in place if your COUNT statement:

(SELECT COUNT(OrderItems.kf_OrderID) 
 FROM OrderItems.kf_OrderID 
 WHERE OrderItems.kf_OrderID=Order.kf_OrderID) AS `Line Item`,