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 [email protected] JER
WHERE JER.TYPE = ‘员工银行卡信息记录‘
AND JER.CREATEDATE = (SELECT MAX(CREATEDATE)
FROM [email protected]
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 [email protected] 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 [email protected] 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 [email protected] 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 [email protected] 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