數據庫環境：SQL SERVER 2005

我們會看到這樣的需求，查詢部門的員工信息和對應的部門人數，要求在同一行上展示。

在沒有分析函數之前，遇到需求，只能通過員工表自關聯來實現。

我這里就有一個類似的例子

SELECT COUNT(*) FROM   dmrpout_03        LEFT JOIN ctlm1210 ctlm1210_id_cgroup ON dmrpout_03. id_cgroup = ctlm1210_id_cgroup.id_cgroup        LEFT JOIN ctlm7161 ctlm7161_id_schtype ON dmrpout_03. id_schtype = ctlm7161_id_schtype .id_schtype        LEFT JOIN ctlm5003 ctlm5003_id_PRoc ON dmrpout_03. id_proc = ctlm5003_id_proc.id_proc        LEFT JOIN ctlm1003 ctlm1003_id_dept ON dmrpout_03. id_dept = ctlm1003_id_dept.id_dept        LEFT JOIN ctlm5111 ctlm5111_id_wkct ON dmrpout_03. id_wkct = ctlm5111_id_wkct.id_wkct        LEFT JOIN ctlm1007 ctlm1007_id_clerk ON dmrpout_03. id_clerk = ctlm1007_id_clerk.id_clerk        LEFT JOIN ctlm3006 ctlm3006_id_stockreas ON dmrpout_03.id_stockreas = ctlm3006_id_stockreas.id_stockreas        LEFT JOIN ctlm3004 ctlm3004_id_keeper ON dmrpout_03. id_keeper = ctlm3004_id_keeper.id_keeper        LEFT JOIN ctlm3001 ctlm3001_id_wh ON dmrpout_03. id_wh = ctlm3001_id_wh.id_wh        LEFT JOIN ctlm5112 ctlm5112_id_pline ON dmrpout_03. id_pline = ctlm5112_id_pline.id_pline        LEFT JOIN ctlm3001 ctlm3001_id_prodwh ON dmrpout_03. id_prodwh = ctlm3001_id_prodwh.id_wh        LEFT JOIN ctlm1005 ctlm1005_id_recorder ON dmrpout_03.id_recorder = ctlm1005_id_recorder.id_user        LEFT JOIN ctlm3002 ctlm3002_id_loc ON dmrpout_03. id_loc = ctlm3002_id_loc.id_loc        LEFT JOIN ctlm3002 ctlm3002_id_prodloc ON dmrpout_03. id_prodloc = ctlm3002_id_prodloc .id_loc        LEFT JOIN v_ctlm2004 v_ctlm2004_id_uom ON dmrpout_03. id_uom = v_ctlm2004_id_uom.id_uom        LEFT JOIN v_ctlm2004 v_ctlm2004_id_secuom ON dmrpout_03.id_secuom = v_ctlm2004_id_secuom.id_uom WHERE  dmrpout_03.line_no = ( SELECT    MIN( line_no)                               FROM     dmrpout_03 b                               WHERE    b .dmrpout_no = dmrpout_03.dmrpout_no                                        AND b .fiscal_year = '2015'                                        AND b .fiscal_period = '6'                                        AND b .id_dept IN (                                        SELECT  id_dept                                        FROM    ctlm1003 ctlm1003_id_dept                                        WHERE   ctlm1003_id_dept.name_dept LIKE '%生產%' )                                        AND b .id_wkct IN (                                        SELECT  id_wkct                                        FROM    ctlm5111 ctlm5111_id_wkct                                        WHERE   ctlm5111_id_wkct.name_wkct LIKE '%儲運%' )                             )        AND dmrpout_03 .fiscal_year = '2015'        AND dmrpout_03 .fiscal_period = '6'        AND ctlm1003_id_dept .name_dept LIKE '% 生產%'        AND ctlm5111_id_wkct .name_wkct LIKE '% 儲運%'

這條SQL要執行4分多鐘才出結果。我們可以從2方面進行優化，第一，SQL里有很多LEFT JOIN，

都是dmrpout_03 LEFT JOIN其它表，如果是一對一關系，則LEFT JOIN后面的表可以省略；

第二，將自連接改寫成分析函數。

改寫后的SQL如下，只耗時12S就出結果了。

SELECT COUNT (*) FROM   ( SELECT    dmrpout_03.line_no ,                    MIN(line_no ) OVER ( PARTITION BY dmrpout_03.dmrpout_no ) AS minline_no          FROM      dmrpout_03                    LEFT JOIN ctlm1003 ctlm1003_id_dept ON dmrpout_03.id_dept = ctlm1003_id_dept.id_dept                    LEFT JOIN ctlm5111 ctlm5111_id_wkct ON dmrpout_03.id_wkct = ctlm5111_id_wkct.id_wkct                    LEFT JOIN ctlm3002 ctlm3002_id_loc ON dmrpout_03.id_loc = ctlm3002_id_loc.id_loc                    LEFT JOIN ctlm3002 ctlm3002_id_prodloc ON dmrpout_03.id_prodloc = ctlm3002_id_prodloc.id_loc                    LEFT JOIN v_ctlm2004 v_ctlm2004_id_uom ON dmrpout_03.id_uom = v_ctlm2004_id_uom.id_uom                    LEFT JOIN v_ctlm2004 v_ctlm2004_id_secuom ON dmrpout_03.id_secuom = v_ctlm2004_id_secuom.id_uom          WHERE     dmrpout_03 .fiscal_year = '2015'                    AND dmrpout_03 .fiscal_period = '6'                    AND dmrpout_03 .id_dept IN (                    SELECT  id_dept                    FROM    ctlm1003 ctlm1003_id_dept                    WHERE   ctlm1003_id_dept .name_dept LIKE '%生產%' )                    AND dmrpout_03 .id_wkct IN (                    SELECT  id_wkct                    FROM    ctlm5111 ctlm5111_id_wkct                    WHERE   ctlm5111_id_wkct .name_wkct LIKE '%儲運%' )        ) t WHERE  t.line_no = minline_no

通過分析函數的改寫，可以減少表的掃描。以后如果遇到類似需求，不妨改成這樣試試。

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