将 Oracle SQL Select 转换为 PostgreSQL select

Question

我有这样的 SQL 语句：

SELECT ABX.ABX_APO_NUMBER,
       COUNT(A1.PROCESS_MODE) AS NUM_PLANNING,
       COUNT(A2.PROCESS_MODE) AS NUM_SETUP,
       COUNT(A3.PROCESS_MODE) AS NUM_OUTPUT
  FROM ABX, USER_INSTANCE U, ACTIVE_PROCESS A1,
       ACTIVE_PROCESS A2, ACTIVE_PROCESS A3
 WHERE U.ABX_APO_NUMBER (+) = ABX.ABX_APO_NUMBER
   AND A1.PROCESS_INSTANCE_NUMBER (+) = U.INSTANCE_NUMBER
   AND A1.PROCESS_MODE (+)= 'PLANNING'
   AND A2.PROCESS_INSTANCE_NUMBER (+) = U.INSTANCE_NUMBER
   AND A2.PROCESS_MODE (+) = 'SETUP'
   AND A3.PROCESS_INSTANCE_NUMBER (+) = U.INSTANCE_NUMBER
   AND A3.PROCESS_MODE (+) = 'OUTPUT'
 GROUP BY ABX.ABX_APO_NUMBER

The (+) is Causeing Fits for PG...我可以删除它们吗？它会意味着同样的事情吗？ Postgres 能理解的等价物是什么？

Answer 1

以下是使用 ANSI-92 JOIN 语法重写的查询：

  SELECT a.abx_apo_number,
         COUNT(ap1.process_mode) AS NUM_PLANNING,
         COUNT(ap2.process_mode) AS NUM_SETUP,
         COUNT(ap3.process_mode) AS NUM_OUTPUT
     FROM ABX a
LEFT JOIN USER_INSTANCE u ON u.abx_apo_number = a.abx_apo_number
LEFT JOIN ACTIVE_PROCESS ap1 ON ap1.process_instance_number = u.instance_number
                            AND ap1.process_mode = 'PLANNING'
LEFT JOIN ACTIVE_PROCESS ap2 ON ap2.process_instance_number = u.instance_number
                            AND ap2.process_mode = 'SETUP'
LEFT JOIN ACTIVE_PROCESS ap3 ON ap3.process_instance_number = u.instance_number
                            AND ap3.process_mode = 'OUTPUT'
 GROUP BY a.abx_apo_number

(+) 是 Oracle 特定的 LEFT OUTER JOIN 语法。要删除它，需要每个 USER_INSTANCE.instance_number 必须具有全部三种处理模式的值：PLANNING、SETUP 和 OUTPUT - 省略其中一项，并且 abx_apo_number 将不会显示在输出。

Answer 2

不，你不能直接删除它们！

(+) 是OUTER JOIN 的旧表示法。

例如

...
  FROM USER_INSTANCE U, ACTIVE_PROCESS A1
 WHERE A1.PROCESS_INSTANCE_NUMBER (+) = U.INSTANCE_NUMBER
   AND A1.PROCESS_MODE (+)= 'PLANNING'
...

必须改为

...
FROM USER_INSTANCE U
LEFT JOIN ACTIVE_PROCESS A1
     ON (     A1.PROCESS_INSTANCE_NUMBER = U.INSTANCE_NUMBER
          AND A1.PROCESS_MODE = 'PLANNING'
        )
...