Oracle case when改写SQL

IT小Chen 2021-04-13

719

---说明：案例来自《收获，不止SQL优化》

创建测试数据：

SQL> drop table t1 purge;
SQL> drop table t2 purge;
SQL> create table t1 as select * from dba_objects ;
SQL> create table t2 as select * from dba_objects ;
SQL> update t2 set status='INVALID' WHERE ROWNUM<=10000;
SQL> update t2 set generated='Y' WHERE ROWNUM<=10000;
SQL> update t2 set temporary='Y' WHERE ROWNUM<=10000;
SQL> update t2 set temporary='M' WHERE temporary<>'Y';
SQL> update t2 set temporary='Q' WHERE temporary<>'Y' or temporary<>'M';
SQL> COMMIT;
SQL> set autotrace traceonly
SQL> set linesize 1000
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原SQL：

SQL>           
select t1.object_name,
       t1.object_id,
       (select count(*)
          from t2
         where temporary = 'Y'
           and t2.object_id = t1.object_id) CNT_TEMPORARY_Y,
       (select count(*)
          from t2
         where created >= sysdate - 365
           and t2.object_id = t1.object_id) CNT_CREATED_NEW,
       (select sum(object_id)
          from t2
         where status <> 'VALUD'
           and t2.object_id = t1.object_id) SUM_OBJID_STATUS_V,
       (select sum(object_id)
          from t2
         where generated = 'Y'
           and t2.object_id = t1.object_id) SUM_OBJID_GENERATED_Y,
       (select sum(object_id)
          from t2
         where generated = 'M'
           and t2.object_id = t1.object_id) SUM_OBJID_GENERATED_M,
       (select sum(object_id)
          from t2
         where generated = 'Q'
           and t2.object_id = t1.object_id) SUM_OBJID_GENERATED_Q
  from t1
 where t1.object_id <= 50;
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case when改造后的SQL：

with w_t2 as
(select
t2.object_id,
count(case when t2.temporary='Y' then 1 end ) CNT_TEMPORARY_Y,
count(case when created >=sysdate-365  then 1 end ) CNT_CREATED_NEW,
sum(case when t2.status<>'VALID' then t2.object_id end ) SUM_OBJID_STATUS_V,
sum(case when t2.generated = 'Y' then t2.object_id end ) SUM_OBJID_GENERATED_Y,
sum(case when t2.generated = 'M' then t2.object_id end ) SUM_OBJID_GENERATED_M,
sum(case when t2.generated = 'Q' then t2.object_id end ) SUM_OBJID_GENERATED_Q
from  t2
group by t2.object_id)
select t1.object_name,t1.object_id,w_t2.* from t1,w_t2
where t1.object_id=w_t2.object_id
and t1.object_id<=50;
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