sql高级用法记录

1.case when then 嵌套用法

2.oracle分组排序取最值

select * from 
(select t.*, row_number() over(partition by 分组字段 order by 排序字段 desc ) rn
from tablename t )
where rn=1

3.遍历树结构数据    3.1 案例1：查询应收单发票及其所有的历史废弃发票 select inv.fileid fileID, inv.pri_inv_no priInvoiceNo, inv.inv_no invoiceNo, inv.inv_dt invDt, inv.act_frt_hire invoiceAmount, case when inv.inv_typ='FREIGHT' then '运费' when inv.inv_typ='HIRE' then '租金' when inv.inv_typ='DEMURRAGE' then '滞期费' when inv.inv_typ='DESPATCH' then '速遣费' when inv.inv_typ='OTHER' then '杂费' else '' end invType, case when inv.inv_status='N' then '正常' when inv.inv_status='A' then '废弃' else '' end invStatus from sh_invoice inv start with inv_no =(select invoiceno from v_sh_cml_incomemanage where fileid='8ae47aa15a93d392015ac5d173b11a52') connect by NOCYCLE prior pri_inv_no = inv_no order by inv.inv_dt desc   3.2 案例2：查找当前发票及其第一第废弃的发票 select inv.inv_no,inv.pri_inv_no, (select distinct inv_no from sh_invoice where pri_inv_no is null start with inv_no = inv.inv_no connect by NOCYCLE prior pri_inv_no = inv_no) firstInvNo from sh_invoice inv where inv.pri_inv_no is not null and inv.inv_status='N'   3.3 案例3：查询截止到指定时间前最近的一张发票 select inv_no, (select distinct inv_no from sh_invoice where rownum=1 and to_char(inv_dt,'yyyy-mm-dd')<='2017-05-17' start with inv_no = inv.inv_no connect by NOCYCLE prior pri_inv_no = inv_no ) lastInvNo from sh_invoice inv where inv.pri_inv_no is not null and inv.inv_status='N' 4.Decode放在join on条件后、放在where条件后的使用方法 4.1 decode放在join on 条件后 left join ( SELECT * FROM ( SELECT t.*, ROW_NUMBER() OVER (PARTITION BY invoiceno ORDER BY trackdate desc,createdate DESC) AS rn FROM sh_inv_track t ) WHERE rn = 1 ) track on track.invoiceno=decode(inv.pri_inv_no,null,inv.inv_no,firstinv.firstInvNo) 4.2 decode放在where条件后 SELECT A.CHECK_INFORM_NO,A.CHECK_NO,SCAN_NUM, B.MODEL_TYPE,B.INTEGRATED_VER,B.INTERNAL_VER FROM SFC.PDI_CHECK_HEAD A LEFT JOIN SFC.PDI_CHECK_INFORM_BILL B ON B.CHECK_INFORM_NO = A.CHECK_INFORM_NO AND B.ENABLED_FLAG = 'Y' AND B.ORGANIZATION_ID = 31 WHERE DECODE(B.MODEL_TYPE,'MBB',B.INTEGRATED_VER,B.INTERNAL_VER) = '集成版本'