通过自关联替代开窗函数实现SQL优化

数据库环境：SQL SERVER 2005

　　我们平时都是通过开窗析函数来取代自关联，减少表扫描，从而优化SQL。今天，反其道而行，

用自关联改写开窗函数。我们先来看一下SQL。

　　原SQL语句

SELECT  * 
FROM    ( SELECT    MIN(a.line_no) OVER ( PARTITION BY a.id_clerk ) AS line_no ,
                    a.dslyipt_no ,
                    a.int_year ,
                    a.int_period ,
                    a.id_scheme ,
                    d.name_scheme ,
                    a.id_schhelp ,
                    e.name_schhelp ,
                    a.id_dept ,
                    b.name_dept ,
                    a.id_clerk ,
                    c.name_clerk ,
                    a.id_slyitem ,
                    a.name_slyitem ,
                    a.dec_value
          FROM      dslyipt_03 a ,
                    ctlm1003 b ,
                    ctlm1007 c ,
                    ctlm7201 d ,
                    ctlm7219 e
          WHERE     a.id_dept = b.id_dept
                    AND a.id_clerk = c.id_clerk
                    AND a.id_scheme = d.id_scheme
                    AND a.id_schhelp = e.id_schhelp
                    AND a.id_scheme = e.id_scheme
        ) dslyipt_03
WHERE   dslyipt_no IN ( '201509000169' )
------------------------相关表的数据量----------------------------------------
SELECT COUNT(*) FROM dslyipt_03 --2321920
SELECT COUNT(*) FROM dslyipt_03 WHERE   dslyipt_no IN ( '201509000169' )--16
SELECT COUNT(*) FROM ctlm1003 --125
SELECT COUNT(*) FROM ctlm1007 --11986
SELECT COUNT(*) FROM ctlm7201 --16
SELECT COUNT(*) FROM ctlm7219 --32

　　dslyipt_03表是大表，有2321920条数据，过滤之后只有16条数据，原SQL总共执行了30多秒才出结果，

因此可以判定，SQL还有优化的余地。

　　对2KW的表进行开窗，慢是有原因的。那么，我们是否可以先过滤再开窗呢？我们来改一下SQL，改写之后

的SQL如下：

SELECT    MIN(a.line_no) OVER ( PARTITION BY a.id_clerk ) AS line_no ,
                    a.dslyipt_no ,
                    a.int_year ,
                    a.int_period ,
                    a.id_scheme ,
                    d.name_scheme ,
                    a.id_schhelp ,
                    e.name_schhelp ,
                    a.id_dept ,
                    b.name_dept ,
                    a.id_clerk ,
                    c.name_clerk ,
                    a.id_slyitem ,
                    a.name_slyitem ,
                    a.dec_value
          FROM      dslyipt_03 a ,
                    ctlm1003 b ,
                    ctlm1007 c ,
                    ctlm7201 d ,
                    ctlm7219 e
          WHERE     a.id_dept = b.id_dept
                    AND a.id_clerk = c.id_clerk
                    AND a.id_scheme = d.id_scheme
                    AND a.id_schhelp = e.id_schhelp
                    AND a.id_scheme = e.id_scheme
                    AND a.dslyipt_no IN ( '201509000169' )

　　嗖的一下，数据就出来了！但是，再核对一下数据，发现字段line_no的数据对不上，说明改错了。改写

后对line_no开窗的范围变小了，所以数据有问题。

　　现在通过自关联来实现开窗函数的功能，自关联改写的SQL如下：

SELECT  f.line_no ,
        a.dslyipt_no ,
        a.int_year ,
        a.int_period ,
        a.id_scheme ,
        d.name_scheme ,
        a.id_schhelp ,
        e.name_schhelp ,
        a.id_dept ,
        b.name_dept ,
        a.id_clerk ,
        c.name_clerk ,
        a.id_slyitem ,
        a.name_slyitem ,
        a.dec_value
FROM    dslyipt_03 a ,
        ctlm1003 b ,
        ctlm1007 c ,
        ctlm7201 d ,
        ctlm7219 e ,
        ( SELECT    a.id_clerk ,
                    MIN(a.line_no) AS line_no
          FROM      dslyipt_03 a
          GROUP BY  a.id_clerk
        ) f
WHERE   a.id_dept = b.id_dept
        AND a.id_clerk = c.id_clerk
        AND a.id_scheme = d.id_scheme
        AND a.id_schhelp = e.id_schhelp
        AND a.id_scheme = e.id_scheme
        AND a.id_clerk = f.id_clerk
        AND a.dslyipt_no IN ( '201509000169' )
OPTION(HASH JOIN)

　　在语句后面，我们通过查询提示，建议SQL走哈希连接，1S之内就出结果了，经核对，数据无误！

　　我们来对比一下改写前后TIME、IO

　　改写前

　　改写后