領導讓我幫忙支援下其他專案的SQL最佳化工作，呦西，是收集案例的好機會。😍
下面SQL都是在不能遠端的情況下，按照原SQL的邏輯等價改寫完成發給現場同學驗證。
案例一
慢SQL，4.32秒：
SELECT MY_.*, RM FROM (SELECT ROWNUM RM, V_.* FROM (SELECT * FROM (select count(1) processidnum, t.processid, t.proc_name_ as procname FROM tkdkdkdk t WHERE 1 = 1 and (t.ASSIGNEE_ = 'server' or exists(select 1 FROM pepepep p WHERE p.task_ = t.ID_ and (p.agent_userid_ = 'server' or (substr(p.groupid_, 6) in (select role_code FROM upupupup WHERE user_code = 'server') or p.userid_ = 'server')))) GROUP BY t.processid, t.proc_name_)) V_ WHERE ROWNUM <= 100000) MY_ WHERE RM >= 1;
慢SQL執行計劃：
改寫最佳化，445ms：
SELECT * FROM (SELECT * FROM (SELECT a.*, rownum rn FROM (SELECT count(1) processidnum, t.processid, t.proc_name_ AS procname FROM tkdkdkdk t LEFT JOIN (SELECT distinct p.task_ FROM pepepep p LEFT JOIN (SELECT role_code FROM upupupup WHERE user_code = 'server' GROUP BY role_code) tsu ON (substr(p.groupid_, 6) = tsu.role_code) WHERE (p.agent_userid_ = 'server' OR (tsu.role_code is NOT null OR p.userid_ = 'server'))) x ON t.ID_ = x.task_ WHERE 1 = 1 AND (t.ASSIGNEE_ = 'server' OR x.task_ is NOT NULL) GROUP BY t.processid, t.proc_name_) a) WHERE rownum <= 100000) WHERE rn >= 1;
改寫最佳化後執行計劃：
最佳化思路：
1、原SQL有很多子查詢，可能會導致計劃走NL，改成JOIN後讓CBO自動判斷是否走HASH還是NL。
2、換了個標準的分頁框架。
案例二
慢SQL，2.6秒：
SELECT MY_.*, RM FROM (SELECT ROWNUM RM, V_.* FROM (SELECT * FROM (select t.*, t.org_code || '-' || t.org_name as codename FROM (select tc.* FROM tgtgtgtg tc start with TC.ORG_ID = '6000001' connect by prior ORG_ID = tc.parent_id) t WHERE org_level <= 3 ORDER BY CASE WHEN ',' || nvl(null, 'fingard') || ',' like '%,' || ORG_ID || ',%' THEN CASE WHEN length(nvl(org_order, '')) = '9' then org_order || '' else '1' || org_code end when length(nvl(org_order, '')) = '9' then '99999999' || org_order || '' else '999999991' || org_code end)) V_ WHERE ROWNUM <= 10) MY_; WHERE RM >= 1;
改寫最佳化一，3.4秒：
SELECT MY_.*, RM FROM (SELECT ROWNUM RM, V_.* FROM (SELECT * FROM (select a.*, a.org_code || '-' || a.org_name as codename FROM (WITH t( lv, codename, ORG_ID, parent_id, org_order, org_code, org_name, org_level ) AS (SELECT 1 as lv, tc.org_code || '-' || tc.org_name AS codename, tc.org_name, tc.ORG_ID, tc.parent_id, tc.org_order, tc.org_code, tc.org_level FROM tgtgtgtg tc WHERE tc.ORG_ID = '6000001' UNION ALL SELECT t.lv + 1, e.org_code || '-' || e.org_name AS codename, e.org_name, e.ORG_ID, e.parent_id, e.org_order, e.org_code, e.org_level FROM tgtgtgtg e INNER JOIN t ON t.ORG_ID = e.parent_id) SELECT * FROM t) a WHERE a.org_level <= 3 ORDER BY CASE WHEN ',' || nvl(null, 'fingard') || ',' like '%,' || ORG_ID || ',%' THEN CASE WHEN length(nvl(org_order, '')) = '9' then org_order || '' else '1' || org_code end when length(nvl(org_order, '')) = '9' then '99999999' || org_order || '' else '999999991' || org_code end)) V_ WHERE ROWNUM <= 10) MY_; WHERE RM >= 1;
使用CTE遞迴改寫方案在PostgreSQL上是個通用的做法，也能取得比較好的效能效果。
但是在OB上反而效果更差點，NL運算元效能不夠強，使用NESTED-LOOP JOIN 效能反而沒有NESTED-LOOP CONNECT BY 運算元好。
OB研發在NESTED-LOOP JOIN運算元上還有繼續最佳化的空間。
改寫最佳化二，1.5秒：
既然使用NL效能不夠理想的情況下，就要想辦法使用HASH來最佳化SQL整體的執行效率。
將自動遞迴的方式改成手動。
1、首先需要知道資料整體的層級有多少。
SELECT DISTINCT lv FROM (SELECT level lv FROM tgtgtgtg tc START WITH TC.ORG_ID = '6000001' CONNECT BY PRIOR ORG_ID = tc.parent_id) t;
2、瞭解到整體的資料是13層，然後使用self join 將不同層級的資料關聯起來。
1 SELECT * 2 FROM (SELECT * 3 FROM (SELECT a.*, rownum rn 4 FROM (SELECT x.* 5 FROM (WITH tgtgtgtg AS 6 (SELECT org_code, org_name, org_id, parent_id, org_order, org_level 7 FROM tgtgtgtg) 8 9 SELECT 1 AS lv, 10 v1.org_code || '-' || v1.org_name AS codename, 11 v1.ORG_ID, 12 v1.parent_id, 13 v1.org_order, 14 v1.org_code, 15 v1.org_level 16 FROM tgtgtgtg v1 17 WHERE v1.ORG_ID = '6000001' 18 19 UNION ALL 20 21 SELECT 2 AS lv, 22 v2.org_code || '-' || v2.org_name AS codename, 23 v2.ORG_ID, 24 v2.parent_id, 25 v2.org_order, 26 v2.org_code, 27 v2.org_level 28 FROM tgtgtgtg v1 29 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 30 WHERE v1.ORG_ID = '6000001' 31 32 UNION ALL 33 34 SELECT 3 AS lv, 35 v3.org_code || '-' || v3.org_name AS codename, 36 v3.ORG_ID, 37 v3.parent_id, 38 v3.org_order, 39 v3.org_code, 40 v3.org_level 41 FROM tgtgtgtg v1 42 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 43 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 44 WHERE v1.ORG_ID = '6000001' 45 46 UNION ALL 47 48 SELECT 4 AS lv, 49 v4.org_code || '-' || v4.org_name AS codename, 50 v4.ORG_ID, 51 v4.parent_id, 52 v4.org_order, 53 v4.org_code, 54 v4.org_level 55 FROM tgtgtgtg v1 56 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 57 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 58 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 59 WHERE v1.ORG_ID = '6000001' 60 61 UNION ALL 62 63 SELECT 5 AS lv, 64 v5.org_code || '-' || v5.org_name AS codename, 65 v5.ORG_ID, 66 v5.parent_id, 67 v5.org_order, 68 v5.org_code, 69 v5.org_level 70 FROM tgtgtgtg v1 71 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 72 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 73 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 74 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 75 WHERE v1.ORG_ID = '6000001' 76 77 UNION ALL 78 79 SELECT 6 AS lv, 80 v6.org_code || '-' || v6.org_name AS codename, 81 v6.ORG_ID, 82 v6.parent_id, 83 v6.org_order, 84 v6.org_code, 85 v6.org_level 86 FROM tgtgtgtg v1 87 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 88 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 89 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 90 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 91 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 92 WHERE v1.ORG_ID = '6000001' 93 94 UNION ALL 95 96 SELECT 7 AS lv, 97 v7.org_code || '-' || v7.org_name AS codename, 98 v7.ORG_ID, 99 v7.parent_id, 100 v7.org_order, 101 v7.org_code, 102 v7.org_level 103 FROM tgtgtgtg v1 104 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 105 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 106 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 107 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 108 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 109 JOIN tgtgtgtg v7 ON v6.ORG_ID = v7.parent_id 110 WHERE v1.ORG_ID = '6000001' 111 112 UNION ALL 113 114 SELECT 8 AS lv, 115 v8.org_code || '-' || v8.org_name AS codename, 116 v8.ORG_ID, 117 v8.parent_id, 118 v8.org_order, 119 v8.org_code, 120 v8.org_level 121 FROM tgtgtgtg v1 122 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 123 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 124 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 125 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 126 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 127 JOIN tgtgtgtg v7 ON v6.ORG_ID = v7.parent_id 128 JOIN tgtgtgtg v8 ON v7.ORG_ID = v8.parent_id 129 WHERE v1.ORG_ID = '6000001' 130 131 UNION ALL 132 133 SELECT 9 AS lv, 134 v9.org_code || '-' || v9.org_name AS codename, 135 v9.ORG_ID, 136 v9.parent_id, 137 v9.org_order, 138 v9.org_code, 139 v9.org_level 140 FROM tgtgtgtg v1 141 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 142 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 143 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 144 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 145 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 146 JOIN tgtgtgtg v7 ON v6.ORG_ID = v7.parent_id 147 JOIN tgtgtgtg v8 ON v7.ORG_ID = v8.parent_id 148 JOIN tgtgtgtg v9 ON v8.ORG_ID = v9.parent_id 149 WHERE v1.ORG_ID = '6000001' 150 151 UNION ALL 152 153 SELECT 10 AS lv, 154 v10.org_code || '-' || v10.org_name AS codename, 155 v10.ORG_ID, 156 v10.parent_id, 157 v10.org_order, 158 v10.org_code, 159 v10.org_level 160 FROM tgtgtgtg v1 161 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 162 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 163 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 164 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 165 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 166 JOIN tgtgtgtg v7 ON v6.ORG_ID = v7.parent_id 167 JOIN tgtgtgtg v8 ON v7.ORG_ID = v8.parent_id 168 JOIN tgtgtgtg v9 ON v8.ORG_ID = v9.parent_id 169 JOIN tgtgtgtg v10 ON v9.ORG_ID = v10.parent_id 170 WHERE v1.ORG_ID = '6000001' 171 172 UNION ALL 173 174 SELECT 11 AS lv, 175 v11.org_code || '-' || v11.org_name AS codename, 176 v11.ORG_ID, 177 v11.parent_id, 178 v11.org_order, 179 v11.org_code, 180 v11.org_level 181 FROM tgtgtgtg v1 182 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 183 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 184 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 185 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 186 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 187 JOIN tgtgtgtg v7 ON v6.ORG_ID = v7.parent_id 188 JOIN tgtgtgtg v8 ON v7.ORG_ID = v8.parent_id 189 JOIN tgtgtgtg v9 ON v8.ORG_ID = v9.parent_id 190 JOIN tgtgtgtg v10 ON v9.ORG_ID = v10.parent_id 191 JOIN tgtgtgtg v11 ON v10.ORG_ID = v11.parent_id 192 WHERE v1.ORG_ID = '6000001' 193 194 UNION ALL 195 196 SELECT 12 AS lv, 197 v12.org_code || '-' || v12.org_name AS codename, 198 v12.ORG_ID, 199 v12.parent_id, 200 v12.org_order, 201 v12.org_code, 202 v12.org_level 203 FROM tgtgtgtg v1 204 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 205 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 206 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 207 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 208 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 209 JOIN tgtgtgtg v7 ON v6.ORG_ID = v7.parent_id 210 JOIN tgtgtgtg v8 ON v7.ORG_ID = v8.parent_id 211 JOIN tgtgtgtg v9 ON v8.ORG_ID = v9.parent_id 212 JOIN tgtgtgtg v10 ON v9.ORG_ID = v10.parent_id 213 JOIN tgtgtgtg v11 ON v10.ORG_ID = v11.parent_id 214 JOIN tgtgtgtg v12 ON v11.ORG_ID = v12.parent_id 215 WHERE v1.ORG_ID = '6000001' 216 217 UNION ALL 218 219 SELECT 13 AS lv, 220 v13.org_code || '-' || v13.org_name AS codename, 221 v13.ORG_ID, 222 v13.parent_id, 223 v13.org_order, 224 v13.org_code, 225 v13.org_level 226 FROM tgtgtgtg v1 227 JOIN tgtgtgtg v2 ON v1.ORG_ID = v2.parent_id 228 JOIN tgtgtgtg v3 ON v2.ORG_ID = v3.parent_id 229 JOIN tgtgtgtg v4 ON v3.ORG_ID = v4.parent_id 230 JOIN tgtgtgtg v5 ON v4.ORG_ID = v5.parent_id 231 JOIN tgtgtgtg v6 ON v5.ORG_ID = v6.parent_id 232 JOIN tgtgtgtg v7 ON v6.ORG_ID = v7.parent_id 233 JOIN tgtgtgtg v8 ON v7.ORG_ID = v8.parent_id 234 JOIN tgtgtgtg v9 ON v8.ORG_ID = v9.parent_id 235 JOIN tgtgtgtg v10 ON v9.ORG_ID = v10.parent_id 236 JOIN tgtgtgtg v11 ON v10.ORG_ID = v11.parent_id 237 JOIN tgtgtgtg v12 ON v11.ORG_ID = v12.parent_id 238 JOIN tgtgtgtg v13 ON v12.ORG_ID = v13.parent_id 239 WHERE v1.ORG_ID = '6000001') x 240 WHERE org_level <= 3 241 ORDER BY CASE 242 WHEN ',' || NVL(NULL, 'fingard') || ',' LIKE '%,' || ORG_ID || ',%' THEN 243 CASE 244 WHEN LENGTH(NVL(org_order, '')) = '9' THEN 245 org_order || '' 246 ELSE '1' || org_code 247 END 248 WHEN LENGTH(NVL(org_order, '')) = '9' THEN 249 '99999999' || org_order || '' 250 ELSE '999999991' || org_code END ) a) 251 WHERE rownum <= 10) 252 WHERE rn >= 1;
現場同學差集比較，確認改寫後的SQL是等價的，執行時間從2.6秒降低到1.5秒能跑出結果。
原來18行的SQL改成了250多行後才最佳化了1秒的執行時間，實在沒其他辦法了，希望OB產研後續能CBO運算元繼續最佳化下。😂😂😂