通过时间戳为多个条目选择最近的行，同时将另一个 table 与当前条目的子字符串连接起来

Question

好吧，标题听起来很复杂，但我真正想做的事情并没有那么复杂。我的表是：

服务状态：

ServiceIdentifier           ServiceStatus   Timestamp

System1-Service1            1               sometimestamp
System1-Service1            1               sometimestamp
System2-Service1            0               sometimestamp
System2-Service1            1               sometimestamp
System1-Service2            1               sometimestamp
System1-Service2            0               sometimestamp
System2-Service2            1               sometimestamp
System2-Service2            1               sometimestamp
System3-Service42           0               sometimestamp

系统名称表：

SystemIdentifier   SystemName

System1            Baconsystem
System2            LoremIpsumSystem
System3            System42

期望的输出：

Baconsystem, Service1, 1, sometimestamp
Baconsystem, Service2, 1, sometimestamp
LoremIpsumSystem, Service1, 1, sometimestamp
LoremIpsumSystem, Service2, 1, sometimestamp
System42, Service42, 0, sometimestamp

SQL 查询 (Oracle) 应该根据时间戳只输出每个 system-service 组合的最新条目。当我试图让每个 system-service 组合只输出一次时，我无法让子字符串上的连接正常工作。感谢任何帮助。

Answer 1

一种可能性是使用函数 substr()、instr()、row_number():

的解决方案

select sn, sv, sst, st 
  from (
    with st as (
      select 
          substr(ServiceIdentifier, 1, instr(ServiceIdentifier, '-')-1) syst,
          substr(ServiceIdentifier, instr(ServiceIdentifier, '-')+1) service, 
          ServiceStatusTable.*
        from ServiceStatusTable)
    select sn.systemname sn, st.service sv, st.servicestatus sst, st.servicetime st,
        row_number() over (partition by systemname, service 
          order by st.servicetime desc) rn
      from st join Systemnametable sn on st.syst = sn.systemidentifier )
  where rn = 1

SQLFiddle

Answer 2

这样做的一种方法是利用 Oracle 正则表达式：

select snt.systemname, sst.service, sst.servicestatus, sst.timestamp
from (select sst.*,
             regexp_substr(ServiceIdentifier, '[^-]+', 1, 1) as system,
             regexp_substr(ServiceIdentifier, '[^-]+', 1, 2) as service,
             row_number() over (partition by ServiceIdentifier
                                order by timestamp desc) as seqnum
      from Servicestatustable sst
     ) sst left join
     Systemnametable snt
     on snt.SystemIdentifier = sst.system
where seqnum = 1;

Here 是此版本的 SQL Fiddle（感谢 Ponder 创建它）。

通过时间戳为多个条目选择最近的行，同时将另一个 table 与当前条目的子字符串连接起来

Selecting the most recent row by timestamp for multiple entries while joining another table with substring of the current one

sql

oracle

select

join

substr