Oracle SQL - Count（*）其中值被多次使用，需要包含NULL

Question

我正在尝试包含一些问题类型由多个ID共享的结果，并且可能在一个ID上包含NULL但在另一个上不包含NULL。示例：EPISY_EMS的问题类型为Client Relations，EPISY_EPISYS也是如此。 EMS product的计数为10且EPISYS product的计数为0，但结果中根本不显示，我如何才能显示为0 Null或Select c.Product_id as [Product ID], b.DESCR as [Product Descr], a.RC_SS_IND as [Self-Service Available], a.RC_SHORT_DESCR as [Problem Type], COUNT(*) as [Count] From PS_RC_CASE c JOIN PS_RC_PROBTYPE_TBL a on c.PROBLEM_TYPE = a.PROBLEM_TYPE AND c.Product_ID = a.Product_ID JOIN PS_PROD_ITEM b on c.PRODUCT_ID = b.PRODUCT_ID WHERE b.EFF_STATUS = 'A' AND c.Creation_Date > '2017-01-01 00:00:00.000' AND a.RC_SS_IND = 'Y' AND a.RC_SHORT_DESCR in ('Client Relations', 'Implementation', 'General Ledger') AND C.Product_ID in ('EPISY_CHOICE', 'EPISY_CKIMRT', 'EPISY_COLDOCTK', 'EPISY_EMS') GROUP BY a.RC_SHORT_DESCR, a.PRODUCT_ID, b.DESCR, a.RC_SS_IND, b.product_id, c.PRODUCT_ID Order By b.DESCR asc ？

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