oracle数据库优化与LNNVL函数使用

一：先谈谈数据库的优化

      1. max 函数 运行速率慢；现在用下面的方式替换

          A;用max函数的方式；获取最新操作时间的 一行员工记录-----------速度慢；

           select *
             from JCT_EMPLID_RECORD@JEHR JER
             WHERE JER.TYPE = '员工银行卡信息记录'
                       AND JER.CREATEDATE = (SELECT MAX(CREATEDATE)
                               FROM JCT_EMPLID_RECORD@JEHR
                                  WHERE TYPE = '员工银行卡信息记录'
                                   AND EMPLID = JER.EMPLID
                           )

           B;不用max函数的方式： ---------------

              SELECT *
                  FROM jct_emplid_record@jehr jer
                  WHERE jer.type = '员工银行卡信息记录'
                  AND NOT EXISTS (SELECT 'X'              //X这里是随意的 可以是任何值   这里的逻辑就是  不存在 比 temp的创建日期大于jer的创建日期；这就是要 jer里的日期是最新的
                       FROM jct_emplid_record@jehr temp
                          WHERE temp.type = jer.type
                            AND temp.emplid = jer.emplid
                            AND temp.createdate > jer.createdate)

    

    二 ：左连接的新写法

           SELECT jer.emplid,
       pn.name,
       to_char(jer.createdate, 'yyyy-mm-dd') createdate,
       pb.account_ec_id,
       ppn.national_id nid
  FROM jct_emplid_record@jehr jer,
       sysadm.ps_pye_bankacct pb,
       sysadm.ps_pers_nid ppn,
       (SELECT ps.emplid, ps.name
          FROM sysadm.ps_names ps
         WHERE NOT EXISTS (SELECT 'X'
                  FROM sysadm.ps_names ps1
                 WHERE ps1.emplid = ps.emplid
                   AND ps1.effdt > ps.effdt)) pn
 WHERE 1 = 1
   AND jer.emplid = ppn.emplid
   AND jer.emplid = pb.emplid(+)    //左连接
   AND jer.emplid = pn.emplid(+)   //左连接
   AND NOT EXISTS
 (SELECT 'X'
          FROM jct_emplid_record@jehr temp
         WHERE temp.type = jer.type
           AND temp.emplid = jer.emplid
           AND temp.createdate > jer.createdate)
   AND jer.type = '员工银行卡信息记录'
   AND ppn.national_id_type = 'NID'
   AND jer.createdate >= to_date('2015-03-01', 'yyyy-mm-dd')
   AND jer.createdate <= to_date('2015-04-10', 'yyyy-mm-dd')
 ORDER BY jer.emplid

三 ：LNNVL函数

   LNNVL官方解释翻译
     lnnvl用于某个语句的where子句中的条件，如果条件为true就返回false；如果条件为UNKNOWN或者false就返回true。该函数不能用于复合条件如AND, OR, or BETWEEN中。

几种情况测试说明

--年份小于2009(lnnvl表示年份大于或者2009包含null)

SQL> select * from xifenfei where lnnvl(year<2009);

 

NAME                       YEAR

-------------------- ----------

xifenfei2008

xifenfei2009               2009

xifenfei2010               2010

xifenfei2011               2011

 

--year不为null(lnnvl表示年份为null)

SQL> select * from xifenfei where lnnvl(year is not null);

 

NAME                       YEAR

-------------------- ----------

xifenfei2008

 

--年份为null(lnnvl表示年份不为null)

SQL> select * from xifenfei where lnnvl(year is  null);

 

NAME                       YEAR

-------------------- ----------

xifenfei2001               2001

xifenfei2002               2002

xifenfei2003               2003

xifenfei2004               2004

xifenfei2005               2005

xifenfei2006               2006

xifenfei2007               2007

xifenfei2009               2009

xifenfei2010               2010

xifenfei2011               2011

 

10 rows selected.

 

--年份为12345(lnnvl表示年份不为12345)

SQL> select * from xifenfei where lnnvl(year =12345);

 

NAME                       YEAR

-------------------- ----------

xifenfei2001               2001

xifenfei2002               2002

xifenfei2003               2003

xifenfei2004               2004

xifenfei2005               2005

xifenfei2006               2006

xifenfei2007               2007

xifenfei2008

xifenfei2009               2009

xifenfei2010               2010

xifenfei2011               2011

 

11 rows selected.

 

--年份不为12345(lnnvl表示年份为12345或者null)

SQL> select * from xifenfei where lnnvl(year !=12345);

 

NAME                       YEAR

-------------------- ----------

xifenfei2008