将Oracle SQL Select转换为PostgreSQL select

Question

我有以下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

（+）导致适合PG ...我可以删除它们，这意味着同一件事吗？Postgres将理解的等效内容是什么？

Answer 1

这是使用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

该(+)是Oracle特定LEFT OUTER JOIN语法。要删除它，将要求每个USER_INSTANCE.instance_number过程模式的值必须均为以下三种：PLANNING，SETUP和OUTPUT-省略一个，并且abx_apo_number将不会显示在输出中。