Question

我有这个查询

SELECT   *
    FROM (SELECT mi.visit_id, mi.event_id, mi.patient_id, mi.mrn, mi.reg_date,
                 mi.d_date, mi.bml_count, mi.TYPE, mblp.baby_patient_id,
                 mblp.baby_birthdate
            FROM ajmid.km0076_motherinfo_test mi LEFT JOIN alfayezb2.mbl_patients mblp
                 ON mblp.mother_patient_id = mi.patient_id
                 --works here 
               AND (   TO_CHAR (mblp.baby_birthdate, 'mm/dd/YYYY') =
                                           TO_CHAR (mi.reg_date, 'mm/dd/YYYY')
                    OR TO_CHAR (mblp.baby_birthdate, 'mm/dd/YYYY') =
                                       TO_CHAR (mi.reg_date - 1, 'mm/dd/YYYY')
                    OR TO_CHAR (mblp.baby_birthdate, 'mm/dd/YYYY') =
                                       TO_CHAR (mi.reg_date + 1, 'mm/dd/YYYY')
                   )
                 ) bml
         LEFT OUTER JOIN --doesn't work here
         (SELECT ROW_NUMBER () OVER (PARTITION BY vis.patient_id ORDER BY vis.admission_date_time)
                                                                          num,
                 vis.admission_date_time, vis.visit_id, vis.patient_id,
                 vis.facility_id
            FROM visit vis) v ON bml.baby_patient_id = v.patient_id
   WHERE v.num = 1
ORDER BY bml.reg_date

bml本身返回118行，而整个查询返回117，原因是bml返回1行，baby_patient_id为null，所以我使用左外连接来显示它，但它仍然没有显示!! < / p>

我该怎么做才能显示bml的所有行？

我使用Toad 9.6

谢谢

Answer 1

可能的原因是你的filter / criteria（where子句）正在为v.num消除一个空值。 WHERE在加入后过滤结果。

 WHERE v.num = 1   -- Are all v.num equal to 1 ?

通过定义NULL意味着对字段使用条件的单纯操作会消除该行，因为无法计算NULL。你可以说“WHERE id！= 1”并期望获得id为null的行，因为null！= 1对吗？错误。 id！= NULL没有逻辑定义。这就是我们在处理NULL时说“IS或IS not NULL”的原因。

Answer 2

检查查询：

SELECT ROW_NUMBER () OVER (PARTITION BY vis.patient_id ORDER BY vis.admission_date_time)
                                                                          num,
                 vis.admission_date_time, vis.visit_id, vis.patient_id,
                 vis.facility_id
            FROM visit vis

它返回118而不是null patient_id＆＃39;

如果它返回117，那可能就是原因。（LEFT OUTER JOIN不会选择两个表都为空的记录）

另外，您确定baby_patient_id表中bml的空值实际上是NULL值而不是空字符吗？（＆＃39;＆＃39;）。

Answer 3

它终于工作了！我添加了

      OR bml.baby_patient_id IS NULL

到where子句，所以最后的脚本是

SELECT   *
FROM (SELECT mi.visit_id, mi.event_id, mi.patient_id, mi.mrn, mi.reg_date,
             mi.d_date, mi.bml_count, mi.TYPE, mblp.baby_patient_id,
             mblp.baby_birthdate
        FROM ajmid.km0076_motherinfo_test mi LEFT JOIN alfayezb2.mbl_patients mblp
             ON mblp.mother_patient_id = mi.patient_id
           AND (   TO_CHAR (mblp.baby_birthdate, 'mm/dd/YYYY') =
                                       TO_CHAR (mi.reg_date, 'mm/dd/YYYY')
                OR TO_CHAR (mblp.baby_birthdate, 'mm/dd/YYYY') =
                                   TO_CHAR (mi.reg_date - 1, 'mm/dd/YYYY')
                OR TO_CHAR (mblp.baby_birthdate, 'mm/dd/YYYY') =
                                   TO_CHAR (mi.reg_date + 1, 'mm/dd/YYYY')
               )
             ) bml
     LEFT OUTER JOIN
     (SELECT ROW_NUMBER () OVER (PARTITION BY vis.patient_id ORDER BY vis.admission_date_time)
                                                                      num,
             vis.admission_date_time, vis.visit_id, vis.patient_id,
             vis.facility_id
        FROM visit vis) v ON bml.baby_patient_id = v.patient_id
    WHERE v.num = 1
      OR bml.baby_patient_id IS NULL
    ORDER BY bml.reg_date

我不知道这有多大帮助，我希望有人能帮我解释一下！谢谢大家

SQL Oracle查询 - 空字段上的左外连接

3 个答案: