MSSQL查询优化（子查询，相关子查询）

Question

无论如何，我可以优化此查询吗？目前运行下面的查询需要半个小时。

我已将其作为子查询尝试并尝试添加Outer Apply，但我发现性能没有任何改善。我将如何改善这种表现？

以下是查询：

SELECT invoiceno,
       dealno,
       customerno,
       vendorno,
       previous1 = (SELECT TOP 1 CASE @Tax
                                   WHEN 0 THEN ( i1.invoicetotal - i1.invoicetax )
                                   ELSE i1.invoicetotal
                                 END
                    FROM   invoiceview i1 WITH (NOLOCK)
                    WHERE  --ii1.orderid=
                     i1.orderid = do.orderid
                     AND i1.invoiceno != i.invoiceno
                     AND i1.billingend < i.billingend
                     AND i1.status NOT IN ( 'ESTIMATE', 'VOID' )
                    ORDER  BY i1.billingend DESC),
       previousstatus1 =(SELECT TOP 1 Rtrim(i1.status)
                         FROM   invoiceview i1 WITH (NOLOCK)
                         --join invoiceitem ii1 with (nolock) on i1.invoiceid = ii1.invoiceid
                         WHERE  --ii1.orderid=
                          i1.orderid = do.orderid
                          AND i1.invoiceno != i.invoiceno
                          AND i1.billingend < i.billingend
                          AND i1.status NOT IN ( 'ESTIMATE', 'VOID' )
                         ORDER  BY i1.billingend DESC)
FROM   invoiceview iv
       LEFT OUTER JOIN dealorder do
                    ON iv.orderid = do.orderid
       LEFT OUTER JOIN invoice i
                    ON iv.invoiceid = i.invoiceid
       LEFT OUTER JOIN deal d
                    ON d.dealid = do.dealid
/*OUTER APPLY ( SELECT TOP 1 RTRIM(i1.status) as previousstatus1, (CASE @Tax WHEN 0 THEN (i1.invoicetotal - i1.invoicetax) ELSE i1.invoicetotal END) as previous1
      FROM invoiceview i1 with (nolock)
      WHERE i1.orderid = do.orderid and i1.invoiceno ! = i.invoiceno and i1.billingend       ) as a */ 

任何帮助都会非常感激。如果没有以前的状态，则previousstatus1查询最多只能在10秒内执行。

Answer 1

感谢所有帮助人员。我弄清楚了这个问题。这是视图。一旦我加入了底层表并实际上做了一个外连接而不是子查询，我注意到了一个很大的区别。