A表：
symbol tdate tclose
000001 20070725 1.23
000002 20070726 0.23
000001 20070723 2.3
000004 20070618 1.4
B表:
symbol
000001
000002
000004
输入2007-07-26
输出
symbol tdate tclose lclose
000001 20070725 1.23 2.3
000002 20070726 0.23 NULL
000004 20070618 1.4 NULL
symbol从B表中取现出,tdate为最新的tclose,
lclose为第二新的tclose,
tclose不为0或NULL
A表的记录数为2000万条左右,现在主要是一个效率的问题.不知道怎么才能再快点.
------解决方案--------------------
说说现在的索引情况
------解决方案--------------------
语句：
select x.*,y.tclose as lclose
from a x left join a y
on a.symbol=b.symbol
and b.tdate=(select max(tdate) from a where symbol=a.symbol and tdate <a.tdate)
where a.tdate <=cast( '2007-7-26 ' as datetime)
and a.tclose <> 0 and a.tclose is not NULL
and not exists (
select 1 from a where symbol=a.symbol
and tdate <=cast( '2007-7-26 ' as datetime)
and tclose <> 0 and tclose is not NULL
and tdate> a.tdate
)
最好有索引(symbol,tdate,tclose)
------解决方案--------------------
晕,我写错了
语句：
select x.*,y.tclose as lclose
from a x left join a y
on x.symbol=y.symbol
and y.tdate=(select max(tdate) from a where symbol=x.symbol and tdate <x.tdate)
where x.tdate <=cast( '2007-7-26 ' as datetime)
and x.tclose <> 0 and x.tclose is not NULL
and not exists (
select 1 from a where symbol=x.symbol
and tdate <=cast( '2007-7-26 ' as datetime)
and tclose <> 0 and tclose is not NULL
and tdate> x.tdate
)
最好有索引(symbol,tdate,tclose)
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要有索引(symbol,tdate,tclose)
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看看这贴，问问这位兄弟
http://community.csdn.net/Expert/topic/5673/5673596.xml?temp=.3719904
------解决方案--------------------
问题没看明白。lclose怎么定义的？
------解决方案--------------------
试试这个.
------------------------------------------------
create table #t (
symbol varchar(10),
tdate varchar(10),
tclose numeric(8,2),
lclose numerice(8,2))
insert #t(symbol,tdate,tclose)
select a.symbol,max(tdate),tclose from a,b where a.symbol=b.symbol