Oracle 12CR2查询转换教程之临时表转换详解

前言

大家都知道在12CR2中出现一种新的查询转换技术临时表转换， 在下面的例子中，数据库对customers表上的子查询结果物化到一个临时表中:

sql> show parameter star_transfORMation_enabled
star_transformation_enabled   string  FALSE
SQL> alter session set star_transformation_enabled='true';

Session altered.

SQL> SELECT c.cust_city,
 2 t.calendar_quarter_desc,
 3 SUM(s.amount_sold) sales_amount
 4 FROM sales s,
 5 times t,
 6 customers c,
 7 channels ch
 8 WHERE s.time_id = t.time_id
 9 AND s.cust_id = c.cust_id
 10 AND s.channel_id = ch.channel_id
 11 AND c.cust_state_province = 'CA'
 12 AND ch.channel_desc = 'Internet'
 13 AND t.calendar_quarter_desc IN ('1999-01','1999-02')
 14 GROUP BY c.cust_city, t.calendar_quarter_desc;
Montara      1999-02  1618.01
Pala       1999-01  3263.93
Cloverdale      1999-01  52.64
Cloverdale      1999-02  266.28
San Francisco     1999-01  3058.27
San Mateo      1999-01  8754.59
Los Angeles     1999-01  1886.19
San Mateo      1999-02  21399.42
Pala       1999-02  936.62
El Sobrante     1999-02  3744.03
El Sobrante     1999-01  5392.34
Quartzhill      1999-01  987.3
Legrand      1999-01  26.32
Pescadero      1999-01  26.32
Arbuckle      1999-02  241.2
Quartzhill      1999-02  412.83
Montara      1999-01  289.07
Arbuckle      1999-01  270.08
San Francisco     1999-02  11257
Los Angeles     1999-02  2128.59
Pescadero      1999-02  298.44
Legrand      1999-02  18.66

22 rows selected.