SQL 有条件地将两个 DB 列之一的结果返回到单个结果列答案

【问题标题】：SQL conditionally return results from one of two DB columns into single result columnSQL 有条件地将两个 DB 列之一的结果返回到单个结果列
【发布时间】：2015-01-01 02:45:17
【问题描述】：

您好，我有以下 SQL 查询，我想有条件地将两个 DB 列（DEA 和 DEA_ALT）之一的结果返回到一个结果列中，具体取决于这两个列中的哪一个被赋值（非空）。数据库设置在其中有两个字段可以存储一个名为 DEA# 的字段，但是两个字段具有相同的目的，因此我想根据哪一列的值返回任一列的结果（可以是任何一个）。

SELECT Distinct t1.UserName,
            t1.[LoginID],
            t7.FirstName, 
            t7.LastName, 
            t7.Title ,
            t7.EndDateOfValidity,      
            NPI = ISNULL(HStaffIdentifiers.Value,''),
            Type= HStaffIdentifiers.Type, 
            DEA=ISNULL(t5.PrescriberCode,''),
            --
            --
            DEA_ALT = ISNULL((select CASE ISNULL(PC.PrescriberCode,'')
                          when '' then ISNULL(HS.Value,'')
                          end
                          from HStaff PC
                          left outer join HStaffIdentifiers HS
                          ON PC.ObjectID = HS.Staff_oid
                          where HS.Type = 'DEA'
                          and HS.Staff_oid = HStaffIdentifiers.Staff_oid
                          ),ISNULL(t5.PrescriberCode,'')),
            --
            --
            Speciality = ISNULL(HDataDictionaryItem3.Description,''),
            Preference_Group = HDataDictionaryItem1.Name
        FROM HSUser t1  with (nolock)
             Left Outer JOIN HStaff t5  with (nolock) 
             ON t1.UserName=t5.MSINumber
             LEFT OUTER JOIN HStaffIdentifiers HStaffIdentifiers WITH (NOLOCK)
             ON t5.ObjectID = HStaffIdentifiers.Staff_oid
             AND HStaffIdentifiers.Type = 'NPI'
             JOIN HPerson t6  with (nolock) 
             ON t5.ObjectID=t6.ObjectID
             JOIN HName t7  with (nolock) 
             ON t6.ObjectID=t7.Person_oid   
             and (t7.EndDateOfValidity < '2010-01-01 00:00:00.000'
                or  t7.EndDateOfValidity is null)

             JOIN HDataDictionaryItem HDataDictionaryItem1 WITH (NOLOCK)
             ON t1.PreferenceGroup_oid = HDataDictionaryItem1.ObjectID
                 AND HDataDictionaryItem1.ItemType_oid = 98

left outer join HDataDictionaryItem HDataDictionaryItem3 WITH (NOLOCK)
             ON t5.PrimarySpeciality_oid = HDataDictionaryItem3.ObjectID
             AND HDataDictionaryItem3.ItemType_oid = 43

             WHERE 

              t1.EndTime >= GETDATE()
             AND t1.BeginTime<=GETDATE()  
             AND t5.Active=1
             AND t6.IsDeleted=0
             AND t5.StaffType = 0 
order by  t7.LastName,  t7.FirstName

来自以下链接的结果片段： http://s7.postimg.org/i5xlsjhnv/12_31_2014_10_00_13_AM.jpg

从查询结果（以红色突出显示）中可以看出，在某些情况下，DEA 可能仅填充在这两列之一中，但是我希望将结果返回到 DEA 列中的单个列，如果它被重视，如果没有，那么我想检查 DEA_ALT 是否被重视，如果是，则将结果返回到这一列。我怎样才能做到这一点？

【问题讨论】：

当两列都被赋值时会发生什么

标签： sql-server

【解决方案1】：

正如@NoDisplayName 所说，您应该只使用coalesce。据我所知，虽然我认为它可以更简单一些。具体来说，如果您希望合并 DEA 和 DEA_ALT，您可以参加此部分

        DEA=ISNULL(t5.PrescriberCode,''),
        --
        --
        DEA_ALT = ISNULL((select CASE ISNULL(PC.PrescriberCode,'')
                      when '' then ISNULL(HS.Value,'')
                      end
                      from HStaff PC
                      left outer join HStaffIdentifiers HS
                      ON PC.ObjectID = HS.Staff_oid
                      where HS.Type = 'DEA'
                      and HS.Staff_oid = HStaffIdentifiers.Staff_oid
                      ),ISNULL(t5.PrescriberCode,'')),

这样写

Coalesce(t5.PrescriberCode, HStaffIden.Value) As DEA,

您需要像这样为 DEA 值添加一个新表

LEFT OUTER JOIN HStaffIdentifiers HStaffIden WITH (NOLOCK)
         ON HStaffIdentifiers.Staff_oid = HStaffIden.Staff_oid

然后你可以采取这个加入条件

LEFT OUTER JOIN HStaffIdentifiers HStaffIdentifiers WITH (NOLOCK)
         ON t5.ObjectID = HStaffIdentifiers.Staff_oid
         AND HStaffIdentifiers.Type = 'NPI'

并像这样删除 AND 条件

LEFT OUTER JOIN HStaffIdentifiers HStaffIdentifiers WITH (NOLOCK)
         ON t5.ObjectID = HStaffIdentifiers.Staff_oid

然后将此条件添加到 where 语句以完成更改

AND HStaffIdentifiers.Type = 'NPI'
And HStaffIden = 'DEA'

编辑：修复了结果集，使其正确匹配您的原始查询

【讨论】：

【解决方案2】：

看起来你只需要Isnull 或coalesce

SELECT ...,Isnull(t5.PrescriberCode, (SELECT CASE Isnull(PC.PrescriberCode, '')
                                           WHEN '' THEN Isnull(HS.Value, '')
                                         END
                                  FROM   HStaff PC
                                         LEFT OUTER JOIN HStaffIdentifiers HS
                                                      ON PC.ObjectID = HS.Staff_oid
                                  WHERE  HS.Type = 'DEA'
                                         AND HS.Staff_oid = HStaffIdentifiers.Staff_oid), Isnull(t5.PrescriberCode, ''))
        ,...

【讨论】：

ISnull 在这种情况下作为子查询运行良好，感谢大家的反馈！