如何复制表避免SQL中的游标?

时间:2011-05-30 09:15:16

标签: sql sql-server tsql sql-server-2008 stored-procedures

我想在SQL中编写脚本,将这两个表(A,B)复制到其他2个表(C,D),结构与A,B相同。

重要

  1. 表C,D NOT 必要为空
  2. 多个进程可以同时调用脚本
  3. 表A具有表B的外键(fk_a_b)

       ________________________  _________________
       |        Table A       |  |   Table B     |  
       |______________________|  |_______________|
       | id     FK_A_B   name |  | id    visible |
       | ----- -------- ------|  | ----- --------|
       | 1      21       n1   |  | 21     true   |
       | 5      32       n2   |  | 32     false  |
       ------------------------  -----------------
    

    假设将表B复制到D后,这就是我得到的

       ________________
       |   Table D    |  
       |______________|
       | id   visible |
       | ----- -------|
       | 51    true   |
       | 52    false  |
       ----------------
    

    现在,当我将表A复制到C时,我需要知道,ID = 21现在映射到ID = 51,ID = 32到ID = 52。最后,表C将是:

       ________________________
       |        Table C       |
       |______________________|
       | id     FK_C_D   name |
       | ----- -------- ------|
       | 61      51       n1  |
       | 62      52       n2  |
       ------------------------
    

    因为几个进程可能同时调用脚本,所以我不能改变表A,B来添加一些辅助列。所以,为了达到这个目的,我使用了CURSOR。我逐行复制了表B和托管临时表,将OldId映射到NewId(21-> 51,32-> 52),然后使用此临时表复制表A.

    我读过CURSOR是不好的做法。那么,还有另一种方法吗?

    谢谢

4 个答案:

答案 0 :(得分:7)

您可以将输出子句与merge语句一起使用,以获取源标识和目标标识之间的映射。 在这个问题中描述。 Using merge..output to get mapping between source.id and target.id

以下是您可以测试的一些代码。我使用表变量而不是真实的表。

设置样本数据:

-- @A and @B is the source tables
declare @A as table
(
  id int,
  FK_A_B int,
  name varchar(10)
)

declare @B as table
(
  id int,
  visible bit
)  

-- Sample data in @A and @B
insert into @B values (21, 1),(32, 0)
insert into @A values (1, 21, 'n1'),(5, 32, 'n2')


-- @C and @D is the target tables with id as identity columns
declare @C as table
(
  id int identity,
  FK_C_D int not null,
  name varchar(10)
)

declare @D as table
(
  id int identity,
  visible bit
)  

-- Sample data already in @C and @D
insert into @D values (1),(0)
insert into @C values (1, 'x1'),(1, 'x2'),(2, 'x3')

复制数据:

-- The @IdMap is a table that holds the mapping between
-- the @B.id and @D.id (@D.id is an identity column)
declare @IdMap table(TargetID int, SourceID int)

-- Merge from @B to @D.
merge @D as D             -- Target table
using @B as B             -- Source table
on 0=1                    -- 0=1 means that there are no matches for merge
when not matched then
  insert (visible) values(visible)    -- Insert to @D
output inserted.id, B.id into @IdMap; -- Capture the newly created inserted.id and
                                      -- map that to the source (@B.id)

-- Add rows to @C from @A with a join to
-- @IdMap to get the new id for the FK relation
insert into @C(FK_C_D, name)
select I.TargetID, A.name 
from @A as A
  inner join @IdMap as I
    on A.FK_A_B = I.SourceID

结果:

select *
from @D as D
  inner join @C as C
    on D.id = C.FK_C_D

id          visible id          FK_C_D      name
----------- ------- ----------- ----------- ----------
1           1       1           1           x1
1           1       2           1           x2
2           0       3           2           x3
3           1       4           3           n1
4           0       5           4           n2

您可以在此处测试代码:http://data.stackexchange.com/stackoverflow/q/101643/using-merge-to-map-source-id-to-target-id

答案 1 :(得分:0)

E.g。 SQL Server将rowguid字段添加到某些发布中包含的用于合并复制的表中。我认为,这种方法可以用在你的任务中。我们的想法是添加几个将扮演pf全局标识符角色的GUID字段,因此我们可以在两个master-datails表对中使用它们

答案 2 :(得分:0)

您可以这样做:

if object_id('tempdb..#TableB') is not null
    drop table #TableB

select identity(int) RowId, *
into #TableB
from TableB

if object_id('tempdb..#TableDIds') is not null
    drop table #TableDIds
create table  #TableDIds (RowId int identity(1,1), Id int)

insert TableD
output inserted.Id into #TableDIds
select Visible
from #TableB
order by RowId

insert TableC
select tdi.Id, ta.name
from TableA ta
    join #TableB tb on
        ta.FK_A_B = tb.Id
    join #TableDIds tdi on
        tdi.RowId = tb.RowId

我使用了以下设置:

create table TableB
(
    Id int not null primary key,
    Visible bit not null
)

create table TableA
(
    Id int not null, 
    FK_A_B int not null foreign key references TableB(Id), 
    Name varchar(10) not null
)

create table TableD
(
    Id int identity(1,1) primary key,
    Visible bit not null
)

create table TableC
(
    Id int identity(1,1), 
    FK_C_D int not null references TableD(Id), 
    Name varchar(10) not null
)

insert TableB
values
    (21, 1),
    (32, 0)

insert TableA
values
    (1, 21, 'n1'),
    (5, 32, 'n2')

答案 3 :(得分:0)