优化有标量子查询的SQL 数据库环境：SQL SERVER 2008R2
今天在数据库中抓出一条比较耗费资源的SQL，只返回904条数据，居然跑了40多分钟。SQL及对应的数据量如下图：
SELECT saft04.cur_year , LEFT(saft04.dept_id, 4) sdept_id , saft04.vdept_id , saft04.dept_id , saft04.fee_id , saft04.vitem_id , ISNULL(saft04.fee_amt, 0) AS saft04_fee_amt , ISNULL(saft04.fee_qty, 0) AS saft04_fee_qty , ISNULL(saft04.fee_amt_flex, 0) AS saft04_fee_amt_flex , ISNULL(saft04.adj_amt, 0) AS saft04_adj_amt , ISNULL(saft04.init_amt, 0) AS saft04_init_amt , ISNULL(saft04.flex_amt, 0) AS saft04_flex_amt , ISNULL(saft04.conf_fee_amt, 0) AS saft04_conf_fee_amt , saft04.fc_app_no , saft04.zone_id , saft04.corr_id , CASE WHEN saft04.fc_app_no < '2010' THEN ( CASE WHEN saft04.flexfapp_flag = 'Y' THEN ISNULL(fee_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) ELSE ISNULL(init_amt, 0) + ISNULL(flex_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) END ) ELSE CASE WHEN b.fee_type2 = '01' OR b.fee_type2 = '02' THEN ISNULL(fee_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) WHEN b.fee_type2 = '03' THEN ISNULL(init_amt, 0) + ISNULL(flex_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) END END bal_amt , ISNULL(( SELECT SUM(b.oPR_amt) FROM v_saft04_fexp b WHERE b.fcapp_id = saft04.fc_app_no ), 0) AS qty1 , CASE WHEN b.fee_type2 = '01' OR b.fee_type2 = '03' THEN ISNULL(saft04.conf_fee_amt, 0) - ( ISNULL(( SELECT SUM(b.opr_amt) FROM v_saft04_fexp b WHERE b.fcapp_id = saft04.fc_app_no ), 0) ) WHEN b.fee_type2 = '02' THEN ISNULL(saft04.init_amt, 0) + ISNULL(saft04.flex_amt, 0) - ISNULL(( SELECT SUM(b.opr_amt) FROM v_saft04_fexp b WHERE b.fcapp_id = saft04.fc_app_no ), 0) + ISNULL(( SELECT SUM(d.opr_amt) FROM v_fadj_rd d WHERE d.fcapp_id = saft04.fc_app_no ), 0) END qty2 , c.base_data2FROM saft04 LEFT JOIN v_ctlm60 b ON b.fee_id = saft04.fee_id LEFT JOIN ctlm1000 c ON c.d_type = 'fee_type2' AND b.fee_type2 = c.base_data1WHERE 1 = 1 AND saft04.com_id = 'LQPJ' AND saft04.cur_year = 2015 AND saft04.dept_id LIKE '2001%' AND ( saft04.dept_id IN ( SELECT dept_id FROM ctlm2000 WHERE user_id1 = '0100030' ) OR '0100030' = 'MANAGER' )ORDER BY saft04.cur_year , saft04.vdept_id , saft04.dept_id , saft04.fee_id , saft04.vitem_id , saft04.zone_id , saft04.corr_id , saft04.fc_app_no-------------------------数据量统计----------------------------------SELECT COUNT(*)FROM saft04WHERE 1 = 1 AND saft04.com_id = 'LQPJ' AND saft04.cur_year = 2015 AND saft04.dept_id LIKE '%2001%' AND ( saft04.dept_id IN ( SELECT dept_id FROM ctlm2000 WHERE user_id1 = '0100030' ) OR '0100030' = 'MANAGER' )--904SELECT COUNT(*) FROM v_saft04_fexp --1262584SELECT COUNT(*) FROM v_fadj_rd d --37077SELECT COUNT(*) FROM v_ctlm60 --431SELECT COUNT(*) FROM ctlm1000 --377
看了一下SQL，有可能出现问题的地方有2个地方，第一个是saft04 表的过滤条件“saft04.dept_id LIKE '%2001%'”使用了模糊查询，导致
走不了既定的索引。经和业务员确定，最开始只是想查询以“2001”开头的单位，因此，这个条件改成“saft04.dept_id LIKE '2001%'”即可。
第二个问题，是最要命的，标量部分“SELECT SUM(b.opr_amt) FROM v_saft04_fexp b WHERE b.fcapp_id = saft04.fc_app_no”走
的执行计划是嵌套循环，因而要改成左联接。
改写后的SQL如下，只执行了23S就全部出结果了。
WITH x0 AS ( SELECT b.fcapp_id , SUM(b.opr_amt) opr_amt FROM v_saft04_fexp b GROUP BY b.fcapp_id ) SELECT saft04.cur_year , LEFT(saft04.dept_id, 4) sdept_id , saft04.vdept_id , saft04.dept_id , saft04.fee_id , saft04.vitem_id , ISNULL(saft04.fee_amt, 0) AS saft04_fee_amt , ISNULL(saft04.fee_qty, 0) AS saft04_fee_qty , ISNULL(saft04.fee_amt_flex, 0) AS saft04_fee_amt_flex , ISNULL(saft04.adj_amt, 0) AS saft04_adj_amt , ISNULL(saft04.init_amt, 0) AS saft04_init_amt , ISNULL(saft04.flex_amt, 0) AS saft04_flex_amt , ISNULL(saft04.conf_fee_amt, 0) AS saft04_conf_fee_amt , saft04.fc_app_no , saft04.zone_id , saft04.corr_id , CASE WHEN saft04.fc_app_no < '2010' THEN ( CASE WHEN saft04.flexfapp_flag = 'Y' THEN ISNULL(fee_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) ELSE ISNULL(init_amt, 0) + ISNULL(flex_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) END ) ELSE CASE WHEN b.fee_type2 = '01' OR b.fee_type2 = '02' THEN ISNULL(fee_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) WHEN b.fee_type2 = '03' THEN ISNULL(init_amt, 0) + ISNULL(flex_amt, 0) + ISNULL(adj_amt, 0) - ISNULL(conf_fee_amt, 0) END END bal_amt , ISNULL(( x0.opr_amt ), 0) AS qty1 , CASE WHEN b.fee_type2 = '01' OR b.fee_type2 = '03' THEN ISNULL(saft04.conf_fee_amt, 0) - ( ISNULL(( x0.opr_amt ), 0) ) WHEN b.fee_type2 = '02' THEN ISNULL(saft04.init_amt, 0) + ISNULL(saft04.flex_amt, 0) - ISNULL(( x0.opr_amt ), 0) + ISNULL(( SELECT SUM(d.opr_amt) FROM v_fadj_rd d WHERE d.fcapp_id = saft04.fc_app_no ), 0) END qty2 , c.base_data2 FROM saft04 LEFT JOIN v_ctlm60 b ON b.fee_id = saft04.fee_id LEFT JOIN ctlm1000 c ON c.d_type = 'fee_type2' AND b.fee_type2 = c.base_data1 LEFT JOIN x0 ON x0.fcapp_id = saft04.fc_app_no WHERE 1 = 1 AND saft04.com_id = 'LQPJ' AND saft04.cur_year = 2015 AND saft04.dept_id LIKE '2001%' AND saft04.dept_id IN ( SELECT dept_id FROM ctlm2000 WHERE user_id1 = '0100030' ) ORDER BY saft04.cur_year , saft04.vdept_id , saft04.dept_id , saft04.fee_id , saft04.vitem_id , saft04.zone_id , saft04.corr_id , saft04.fc_app_no
改写后的SQL还有一个标量子查询没处理，改写的思路和上面一样，因执行时间已经缩短到23S，就不改了。