又一次遇到了这个问题。Access里执行left join联合查询，总是提示：至少一个参数未指定的错误

首先，每次联合查询都需要用圆括号括起来：

Select * FROM (aa LEFT JOIN bb ON aa.a = bb.a ) LEFT JOIN cc ONcc.a = bb.a;

注意：在使用join语句查询时，如果有加多个On条件，必须用括号括起来，如：

Select * FROM (aa LEFT JOIN bb ON aa.a=bb.a) LEFT JOIN cc ON(bb.a=cc.a and bb.b=cc.b) 

其他例子可以参考：

1、Select * FROM URL as a LEFT OUTER JOIN MobileAfter as b ON a.URL = b.URL

2、Select * FROM (URL as a LEFT OUTER JOIN MobileAfter as b ON a.URL= b.URL) LEFT OUTER JOIN MobileBefore as c ONc.URL=a.URL

3、Select * INTO Ttable1 FROM ((((URL as a

LEFT OUTER JOIN MobileAfter as b ON a.URL=b.URL) 

LEFT OUTER JOIN MobileBefore as c ON c.URL=a.URL) 

LEFT OUTER JOIN TeleCOM as d ON d.URL=a.URL) 

LEFT OUTER JOIN UniCOM as e ON e.URL=a.URL)