SQL 连接给出错误的计数

Question

我在下面有一个用非 ansi 编写的查询，我正在转换为 ansi 以便从 SQL 2008 迁移到 2012。问题是以下查询的计数不匹配。

 Select  count(*) 
 FROM t1 ,t2 ,t3,t4,t5
 WHERE t3.RequestId = t1.GenRequestId
 AND t1.RequestType = 'xxx'
 AND t4.RequestId =* t3.RequestId
 AND t4.ItemTypeId =* t2.ItemTypeId 
 AND t1.managerid *= t5.managerid 

 Select  count(*)
 FROM t1
 LEFT JOIN t5 ON t1.managerid = t5.managerid,
 t4
 RIGHT JOIN t3 ON t4.RequestId = t3.RequestId
 RIGHT JOIN t2 ON t4.ItemTypeId = t2.ItemTypeId
 WHERE t3.RequestId = t1.GenRequestId
 AND t1.RequestType = 'xxx' 

在使用连接时我想要相同的计数。感谢您的帮助..!!

Answer 1

要解决这个问题，请重写原始内容，使所有内容都是左外连接：

Select  count(*) 
 FROM t1 ,t2 ,t3,t4,t5
 WHERE t3.RequestId = t1.GenRequestId
 AND t1.RequestType = 'xxx'
 AND t3.RequestId *= t4.RequestId
 AND t2.ItemTypeId *= t4.ItemTypeId 
 AND t1.managerid *= t5.managerid ;

然后使用此建议的顺序进行最终查询（左侧的表格需要出现在右侧的表格之前）：

 SELECT  count(*)
 FROM t1 INNER JOIN
      t3
      ON t3.RequestId = t1.GenRequestId LEFT OUTER JOIN
      t4
      ON t3.RequestId = t4.RequestId LEFT OUTER JOIN
      t2
      ON t2.ItemTypeId = t4.ItemTypeId LEFT OUTER JOIN
      t5
      ON t1.managerid = t5.managerId;
 WHERE t1.RequestType = 'xxx';

不过，老实说，我发现旧式连接语法很难使用。而且，我发现混合使用left outer join 和right outer join 真的很困难。我倾向于回到数据并从头开始重写查询。