数据库环境：SQL SERVER 2005
我们会看到这样的需求，查询部门的员工信息和对应的部门人数，要求在同一行上展示。
在没有分析函数之前，遇到需求，只能通过员工表自关联来实现。
我这里就有一个类似的例子
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 '%生产%' ) AND b .id_wkct IN ( SELECT id_wkct FROM ctlm5111 ctlm5111_id_wkct WHERE ctlm5111_id_wkct.name_wkct LIKE '%储运%' ) ) AND dmrpout_03 .fiscal_year = '2015' AND dmrpout_03 .fiscal_period = '6' AND ctlm1003_id_dept .name_dept LIKE '% 生产%' AND ctlm5111_id_wkct .name_wkct LIKE '% 储运%'
这条SQL要执行4分多钟才出结果。我们可以从2方面进行优化，第一，SQL里有很多LEFT JOIN，
都是dmrpout_03 LEFT JOIN其它表，如果是一对一关系，则LEFT JOIN后面的表可以省略；
第二，将自连接改写成分析函数。
改写后的SQL如下，只耗时12S就出结果了。
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 '%生产%' ) AND dmrpout_03 .id_wkct IN ( SELECT id_wkct FROM ctlm5111 ctlm5111_id_wkct WHERE ctlm5111_id_wkct .name_wkct LIKE '%储运%' ) ) t WHERE t.line_no = minline_no
通过分析函数的改写，可以减少表的扫描。以后如果遇到类似需求，不妨改成这样试试。
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