ORACLE查询当前资产状态，和另一个数据库联查，（查询重复数据中第一条），子查询作为字段查询

背景：ORACLE查询当前资产状态，包含资产信息（表1），资产维修状态（表2），资产报废状态（表3）

如下：

资产信息：

资产维修：

资产报废：

资产申请完了以后可以申请当前资产的维修和报废，其中维修有两个流程，一个是申请维修，然后维修。对应的都需要启动相应的流程去申请维修或者报废

流程表如下：

查询当前所有的资产以及对应的资产状态（维修状态，报废状态）：sql语句如下：

select t.ASSET_ID             as assetId,
       t.ASSET_NAME           as assetName,
       t.ASSET_SORT           as assetSort,
       t.ASSET_MODEL          as assetModel,
       t.BIRTH_DATE           as birthDate,
       t.INTERNATIONAL_NUMBER as internationalNumber,
       t.MANUFACTURER         as manufacturer,
       t.PURCHASE_DATE        as purchaseDate,
       t.NET_SALVAGE          as netSalvage,
       t.EXPECTED_YEAR        as expectedYear,
       t.NET_VALUE            as netValue,
       t.ORIGINAL_VALUE       as originalValue,
       t.DEPRECIATION_METHOD  as depreciationMethod,
       t.SERVICE_CONDITION    as serviceCondition,
       t.STOREMAN             as storeMan,
       t.REMARK               as remark,
       t.ADD_TYPE             as addType,
       t.PROCESSINSTANCEID    as processinstanceId,
       t.CUSTODY_DEPT         as custodyDept,
       t.USED_YEAR            as usedYear,
       t.ID                   as Id,
       m.status               as clearStatus,
       --  nn.status              as maintainStatus,
       (select a.status
          from (select a.asset_id, b.status
                  from asset_maintain a
                  join workflow.workflow_execution b
                    on b.processinstanceid = a.processinstanceid
                 order by b.create_time desc) a
         where a.asset_id = t.asset_id
           and rownum = 1) as maintainStatus
  from ASSET_INFO t
  left join (select *
               from ASSET_CLEAR c
               join workflow.workflow_execution n
                 on c.processinstanceid = n.processinstanceid) m
    on t.asset_id = m.asset_id

重点是这里：

领悟：子查询可以作为业务字段使用，同时可以根据当前主查询的表进行相关联，取出自己想要的数据