有些複雜的SQL

<1>
Q:一個表， 包含完全相同重複數據若干，怎麼刪除多餘記錄:
A:
  ORACLE的ROWID   AND   ROWNUM   
1.ORACLE中是非常容易解決的，用ROWID就行了。   
  delect   from   mytable   x   
  where   rowid   <>   (select   max(rowid)   
                                      from   mytable   y   
                                    where   y.field1   =   x.field1   
                                        and   y.field2   =   x.field2   
                                        .....   
                                  );   
2.存儲過程：
create   procedure   sp_cleardata   
  as   
  begin   
      begin   tran     
        insert   into   table   #b   select   distinct   *   from   table_a     
    
        delete   from   table_a   
      
        insert   into   table_a   select   *   from   #b     
      commit   tran   
  end   
3.可以用遊標:
  給你個例子     
  drop   table   userinfo   
  create   table   userinfo   
  (   
        username   char(10),   
        sex   char(4),   
        phone   char(10)   
  )   
    
  insert   userinfo   select   'aaa','男','12300'   union   all   
                                  select   'bbb','男','12300'   union   all   
                                  select   'aaa','男','12300'   union   all   
                                  select   'bbb','男','12300'   union   all   
                                  select   'aaa','男','12300'   union   all   
                                  select   'ccc','男','12300'   union   all   
                                  select   'aaa','男','12300'     
    
  --(1)定義   
  declare   delcur   cursor   
  for     select   count(*)   as   num   ,username   from   userinfo   
            group   by   username   
    
  --(2)打開   
  open   delcur   
    
  --(3)操作   
  declare   @num   int,@name   varchar(10)   
  fetch   next   from   delcur   into   @num,@name   
  while(@@fetch_status=0)   
  begin   
            declare   second   cursor   for   select   *   from   userinfo   where   username=@name   
              
            open   second   
              
            fetch   next   from   second   
            while(@num   >1)   
            begin   
                  delete   from   userinfo   where   current   of   second   
                  set   @num=@num-1   
                  fetch   next   from   second   
            end   
            close   second   
            deallocate   second   
            fetch   next   from   delcur   into   @num,@name   
  end   
    
  close   delcur   
  deallocate   delcur

<2>
Q:如何在一表中用一SQL語句查詢出兩條完全相同的記錄:
A:
select   col1,col2,col3...   
from   t   
group   by   col1,col2,col3...   
having   count(*)>1

<3>
Q:刪除一個表中所有與另一個表完全相同的記錄
A:    
delete   from   t1       where   exists(select   1   from   t2   b   where   t1.f1=b.f1   and   t1.f2=b.f2)
delete   表1   
  from   表1   a,表2   b   where   a.col1=b.col1   and   a.col2=b.col2   and   ...--所有關連字段

delete   from   表1   where   checksum(*)   in(select   checksum(*)   from   表2)
  checksum生成一行數據的hash值



分組算法1：
create table #table1
(hzh char(2),
 kwh char(2),
 zl  datetime,
 spmc char (4))

insert into #table1 (hzh,kwh,zl,spmc) values('aa','bb','2001-5-6 00:01:001','1111')
insert into #table1 (hzh,kwh,zl,spmc) values('aa','bb','2001-5-6 00:02:002','2222')
insert into #table1 (hzh,kwh,zl,spmc) values('aa','bc','2001-5-6 00:03:003','3333')
insert into #table1 (hzh,kwh,zl,spmc) values('aa','bc','2001-5-6 00:04:004','4444')
insert into #table1 (hzh,kwh,zl,spmc) values('ab','bb','2001-5-6 00:05:005','5555')

select #table1.hzh, #table1.kwh, #table1.zl, #table1.spmc
from #table1,
(
select hzh,kwh,max(zl) as zl
from #table1
group by hzh,kwh) t
where #table1.zl = t.zl

select * from #table1


drop table #table1



分組算法2：
create table #table1
(hzh char(2),
 kwh char(2),
 zl  int,
 spmc char (4))

insert into #table1 (hzh,kwh,zl,spmc) values('aa','bb',3,'1111')
insert into #table1 (hzh,kwh,zl,spmc) values('aa','bb',4,'2222')
insert into #table1 (hzh,kwh,zl,spmc) values('aa','bc',5,'3333')
insert into #table1 (hzh,kwh,zl,spmc) values('aa','bc',6,'4444')
insert into #table1 (hzh,kwh,zl,spmc) values('ab','bb',7,'5555')

select #table1.hzh, #table1.kwh, #table1.zl, #table1.spmc
from #table1,
(
select hzh,kwh,max(zl) as zl
from #table1
group by hzh,kwh) t
where #table1.zl = t.zl and #table1.hzh=t.hzh and #table1.kwh=t.kwh

select * from #table1


drop table #table1




解決了代碼和名稱對應的問題,還有case when 語句得使用和別名得好處

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 SELECT  (
          case (select distinct T_TRAIN.Fld_Depart_Train_Code from T_TRAIN where T_TRAIN.Fld_Train_Code=T_TRAIN_SEGMENT_RELATION.Fld_Train_Code)
               when null then  T_TRAIN_SEGMENT_RELATION.Fld_Train_Code 
               else (select distinct T_TRAIN.Fld_Depart_Train_Code from T_TRAIN where T_TRAIN.Fld_Train_Code=T_TRAIN_SEGMENT_RELATION.Fld_Train_Code)
          end    ) as Train_Code,
         T_TRAIN_SEGMENT_RELATION.Fld_Segment_Code,  
         d1.Fld_Station_Name,  
         d2.Fld_Station_Name,   
         T_TRAIN_SEGMENT_RELATION.Fld_Segment_Distance,  
         T_TRAIN_SEGMENT_RELATION.Fld_Engine_Dep_Name,  
         T_TRAIN_SEGMENT_RELATION.Fld_Owner_Dep_Name,  
         (select distinct Fld_Engine_Type_Name  from T_ENGINE_DEP where T_TRAIN_SEGMENT_RELATION.Fld_Engine_Type=T_ENGINE_DEP.Fld_Engine_Type) as Fld_Engine_Type
    FROM T_TRAIN_SEGMENT_RELATION   , T_STATION d1 , T_STATION d2
    where T_TRAIN_SEGMENT_RELATION.Fld_Segment_Start_Station_Code=d1.Fld_Station_Code and
          T_TRAIN_SEGMENT_RELATION.Fld_Segment_End_Station_Code=d2.Fld_Station_Code ;

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對遊標進行更新得操作：

create procedure collection_train as
declare @Fld_Segment_Code Char(10)
declare @Fld_Segment_Start_Station Char(20),@Fld_Segment_End_Station Char(20)
declare @Start_Fld_Station_Code Char(4),@End_Fld_Station_Code Char(4)
declare @i int
select @i=0

declare cur_result cursor for
Select Fld_Segment_Code,Fld_Segment_Start_Station,Fld_Segment_End_Station from T_TRAIN_SEGMENT_RELATION
for update of Fld_No
open cur_result

fetch cur_result into @Fld_Segment_Code,@Fld_Segment_Start_Station,@Fld_Segment_End_Station

while @@sqlstatus = 0
begin
      select @i=@i+1
      update T_TRAIN_SEGMENT_RELATION set Fld_No=@i                          
      where current of  cur_result
     
     

      fetch cur_result into @Fld_Segment_Code,@Fld_Segment_Start_Station,@Fld_Segment_End_Station

end

close cur_result

deallocate cursor cur_result  ;