仅从SQL查询获取第一行

Question

您好，我在使用以下查询获取前1行时遇到了麻烦。 它在oracle，plsql中。

SELECT per.person_no, 
       perbus.person_no, 
       perbus.edit_dt, 
       perbus.org_name, 
       perbus.FIRST_NAME 
FROM users.persons per
    LEFT OUTER JOIN (
        SELECT ASSOC.edit_dt,PER_CONTACTS.PERSON_NO, 
               PER_CONTACTS.PERSON_ID AS PER_ID,
               PER.EXTERNAL_PERSON_ID AS EXT_PER_ID,
               PER_CONTACTS.LNAME||', '||PER_CONTACTS.FNAME AS NAME, 
               PER_CONTACTS.FNAME AS FIRST_NAME, 
               PER_CONTACTS.MNAME AS MIDDLE_NAME, 
               PER_CONTACTS.LNAME AS LAST_NAME,
               ORG.ORG_NAME AS ORG_NAME,
               T_ORG.ORG_ID AS ORG_ID,
               T_ORG.ORG_DISPLAY_ID AS EXT_ORG_ID,
               rownum AS rn
        FROM USERS.PER_CONTACTS PER_CONTACTS
            LEFT OUTER JOIN USERS.PERSONS PER ON PER.PERSON_ID = PER_CONTACTS.PERSON_ID
            LEFT OUTER JOIN USERS.ASSOC ASSOC ON ASSOC.PERSON_ID = PER.PERSON_ID
            LEFT OUTER JOIN USERS.T_ORG T_ORG ON T_ORG.T_ORG_ID = ASSOC.T_ORG_ID
            LEFT OUTER JOIN USERS.ORG ORG ON ORG.ORG_ID = T_ORG.ORG_ID
        WHERE PER_CONTACTS.CONTACT_ROLE_LOV = 'EMPLOYEE' AND PER_CONTACTS.PERSON_NO IN (SELECT PERSON_NO FROM USERS.QA_APPROVED)
        ORDER BY ASSOC.edit_dt DESC
    ) 
    perbus ON perbus.PERSON_NO = PER.PERSON_NO 
WHERE PER.PERSON_NO IN (SELECT PERSON_NO FROM USERS.QA_APPROVED)

我是oracle的新手，在上面的查询中，由于数据的缘故，我得到了重复-我需要根据Assoc.edit_dt获取第一条记录。

我可以通过Assoc.edit_dt对记录进行排序，但是当我在Join内使用诸如where row_num = 1的子句时，所有perbus表字段的输出查询都为null。

请指教。

Answer 1

尝试这个

如果您想按PERSON_NO返回TOP 1行，则

更换

rownum as rn

与

ROW_NUMBER() OVER (PARTITION BY PER_CONTACTS.PERSON_NO 
                    ORDER BY ASSOC.edit_dt DESC) RN

如果您想整体返回TOP 1，则

更换

rownum as rn

与

ROW_NUMBER() OVER (ORDER BY ASSOC.edit_dt DESC) RN

最后，在您的外部where子句中，仅执行RN = 1来选择顶部的1行

WHERE PER.PERSON_NO IN (select PERSON_NO from USERS.QA_APPROVED) AND RN = 1

Answer 2

您可以使用结果偏移量并获取第一个子句 （仅适用于12c）

只需添加

FETCH FIRST ROW ONLY;

在order by子句之后

有关更多信息。 读这个

希望这可以帮助=）

编辑：

SELECT per.person_no, 
       perbus.person_no, 
       perbus.edit_dt, 
       perbus.org_name, 
       perbus.FIRST_NAME 
FROM users.persons per
    LEFT OUTER JOIN (
        SELECT ASSOC.edit_dt AS EDIT_DT,PER_CONTACTS.PERSON_NO, 
               PER_CONTACTS.PERSON_ID AS PER_ID,
               PER.EXTERNAL_PERSON_ID AS EXT_PER_ID,
               PER_CONTACTS.LNAME||', '||PER_CONTACTS.FNAME AS NAME, 
               PER_CONTACTS.FNAME AS FIRST_NAME, 
               PER_CONTACTS.MNAME AS MIDDLE_NAME, 
               PER_CONTACTS.LNAME AS LAST_NAME,
               ORG.ORG_NAME AS ORG_NAME,
               T_ORG.ORG_ID AS ORG_ID,
               T_ORG.ORG_DISPLAY_ID AS EXT_ORG_ID,
               rownum AS rn
        FROM USERS.PER_CONTACTS PER_CONTACTS
            LEFT OUTER JOIN USERS.PERSONS PER ON PER.PERSON_ID = PER_CONTACTS.PERSON_ID
            LEFT OUTER JOIN USERS.ASSOC ASSOC ON ASSOC.PERSON_ID = PER.PERSON_ID
            LEFT OUTER JOIN USERS.T_ORG T_ORG ON T_ORG.T_ORG_ID = ASSOC.T_ORG_ID
            LEFT OUTER JOIN USERS.ORG ORG ON ORG.ORG_ID = T_ORG.ORG_ID
        WHERE PER_CONTACTS.CONTACT_ROLE_LOV = 'EMPLOYEE' AND PER_CONTACTS.PERSON_NO IN (SELECT PERSON_NO FROM USERS.QA_APPROVED)
        --ORDER BY ASSOC.edit_dt DESC
    ) 
    perbus ON perbus.PERSON_NO = PER.PERSON_NO 
WHERE PER.PERSON_NO IN (SELECT PERSON_NO FROM USERS.QA_APPROVED)
ORDER BY perbus.edit_dt DESC 
FETCH FIRST ROW ONLY;

仅供参考，您为所有列提供了别名，除了一个别名assoc.edit_dt，但是您在主查询中调用它的方式就像它具有别名一样。因此，我采取了特权为assoc.edit_dt添加别名

Answer 3

在这里使用解析函数肯定会解决您的问题。基于person_id和Assoc_edt_dt，我们只能提取一条具有最大/最小行的记录。 以下是您可以尝试的代码段。 希望能帮助到你

SELECT per.person_no,
  perbus.person_no,
  perbus.edit_dt,
  perbus.org_name,
  perbus.FIRST_NAME
FROM users.persons per
LEFT OUTER JOIN
  (SELECT ASSOC.edit_dt,
    PER_CONTACTS.PERSON_NO,
    PER_CONTACTS.PERSON_ID AS PER_ID,
    PER.EXTERNAL_PERSON_ID AS EXT_PER_ID,
    PER_CONTACTS.LNAME
    ||', '
    ||PER_CONTACTS.FNAME AS NAME,
    PER_CONTACTS.FNAME   AS FIRST_NAME,
    PER_CONTACTS.MNAME   AS MIDDLE_NAME,
    PER_CONTACTS.LNAME   AS LAST_NAME,
    ORG.ORG_NAME         AS ORG_NAME,
    T_ORG.ORG_ID         AS ORG_ID,
    T_ORG.ORG_DISPLAY_ID AS EXT_ORG_ID,
    ROW_NUMBER() OVER(PARTITION BY PER_CONTACTS.PERSON_ID ORDER BY ASSOC.edit_dt DESC) rn
  FROM USERS.PER_CONTACTS PER_CONTACTS
  LEFT OUTER JOIN USERS.PERSONS PER
  ON PER.PERSON_ID = PER_CONTACTS.PERSON_ID
  LEFT OUTER JOIN USERS.ASSOC ASSOC
  ON ASSOC.PERSON_ID = PER.PERSON_ID
  LEFT OUTER JOIN USERS.T_ORG T_ORG
  ON T_ORG.T_ORG_ID = ASSOC.T_ORG_ID
  LEFT OUTER JOIN USERS.ORG ORG
  ON ORG.ORG_ID                       = T_ORG.ORG_ID
  WHERE PER_CONTACTS.CONTACT_ROLE_LOV = 'EMPLOYEE'
  AND PER_CONTACTS.PERSON_NO         IN
    (SELECT PERSON_NO FROM USERS.QA_APPROVED
    )
  ORDER BY ASSOC.edit_dt DESC
  ) perbus ON perbus.PERSON_NO = PER.PERSON_NO
WHERE PER.PERSON_NO           IN
  (SELECT PERSON_NO FROM USERS.QA_APPROVED
  )
AND perbus.rn = 1;

Answer 4

要从数据集中仅获取“很少”记录，您可以使用“ rownum”-这里是一个示例：

select * from user_tables where rownum < 4

另一个示例（根据“ table_name”选择前2行）：

select * from (select * from user_tables order by table_name) where rownum<3

注意：请勿使用等号（ = ），而必须使用（ < ）。