Question

我正在尝试从Oracle转换此代码：

CREATE VIEW PLANNED AS
SELECT ASP.ASP_SPACE_NM,
       SUM(MO.MO_TKR_TOTAL_OFF_SCHEDULED) "TOTAL_PLANNED"
  FROM OBJECTIVE MO, SPACE ASP
 WHERE ASP.ASP_SPACE_NM = MO.ASP_SPACE_NM (+)
   AND MO.MO_MSN_CLASS_NM = 'EPIC'
 GROUP BY ASP.ASP_SPACE_NM

致Postgres。

这两行令我困惑：

   SUM(MO.MO_TKR_TOTAL_OFF_SCHEDULED) "TOTAL_PLANNED"

这和这个一样吗？

   SUM(MO.MO_TKR_TOTAL_OFF_SCHEDULED) AS TOTAL_PLANNED

我不知道（+）在这一行中意味着什么：

 WHERE ASP.ASP_SPACE_NM = MO.ASP_SPACE_NM (+)

Answer 1

那是老派，Oracle特有的LEFT JOIN语法。您想将其替换为：

CREATE VIEW PLANNED AS
   SELECT s.asp_space_nm,
          SUM(o.mo_tkr_total_off_scheduled) 'total_planned'
     FROM SPACE s
LEFT JOIN OBJECTIVE o ON o.asp_space_nm = s.asp_space_nm 
                     AND o.mo_msn_class_nm = 'EPIC'
 GROUP BY s.asp_space_nm

参考：

Oracle LEFT JOIN

Answer 2

+表示（编辑：左）外部联接。

并且

SUM(MO.MO_TKR_TOTAL_OFF_SCHEDULED) "TOTAL_PLANNED"

确实很可能与

相同

SUM(MO.MO_TKR_TOTAL_OFF_SCHEDULED) as "TOTAL_PLANNED"

如果我没记错，PostgreSQL中并不真正需要as（尽管在我看来它更明确了）。

您可以查看Postgresql维基上的以下页面，了解更多差异：Oracle to Postgres conversion。

Postgres帮助的Oracle语法

2 个答案: