我知道,当我将一行插入到具有标识列的表中时,我可以使用SELECT @@IDENTITY
来检索刚插入的行的标识。SQL Server是否具有返回多个值的@@ IDENTITY?
如果我做了一个插入10行到同一个表的插入语句,是否有一种实用的方法来获得所有10行的ID?
我知道,当我将一行插入到具有标识列的表中时,我可以使用SELECT @@IDENTITY
来检索刚插入的行的标识。SQL Server是否具有返回多个值的@@ IDENTITY?
如果我做了一个插入10行到同一个表的插入语句,是否有一种实用的方法来获得所有10行的ID?
是的,使用OUTPUT子句。无论如何,你应该使用它作为第一选择。
更好的是,您可以使用OUTPUT返回多个字段。所以你可以使用代理键和自然键来扩充一个表变量。
带有INSERT的OUTPUT子句缺少:在插入源表中为每个行分配Id后无法说出。
declare @Persistent table (Id int not null identity primary key, Value varchar(10));
declare @Temporary table (Id int not null primary key, Value varchar(10));
insert into @Temporary values (11, 'AAA'), (22, 'AAA'), (33, 'CCC');
insert into @Persistent (Value)
output inserted.Id
select Value from @Temporary;
在上面的例子中,我们将得到@Persistent表实际ID列表,但我们不能在@Temporary表的ID映射到IDS,因为OUPTUT在INSERT不允许获得源表中的字段 - 它只获取INSERTED表格字段。
与INSERT相反,MERGE中的OUPTUT子句允许从源表中获取字段。因此,使用与合并输出解决了这个问题:
merge into @Persistent as target
using @Temporary as source on source.Id = target.Id
when matched then
update set Value = source.Value
when not matched then
insert (Value) values (Value)
output
inserted.Id, source.Id;
以下是使用MERGE命令插入,更新,删除父子表中的行例。从MERGE OUTPUT收集目标源映射非常有用:
-- definition of persistent tables
declare @Parents table (Id int not null identity primary key, Name varchar(10));
declare @Children table (Id int not null identity primary key, ParentId int, Name varchar(10));
-- imagine that persistent tables contain some data
insert into @Parents (Name) select 'Alfa';
insert into @Children (ParentId, Name) select 1, 'Delta';
-- definition of temporary tables
declare @TempParents table (Id int not null primary key, Name varchar(10));
declare @TempChildren table (Id int not null primary key, ParentId int, Name varchar(10));
-- data to insert (with negative Ids) and update (with real positive Ids)
insert into @TempParents values
(1, 'Alpha'), (-2, 'Bravo'), (-1, 'Charlie');
insert into @TempChildren values
(-9, 1, 'Alpha-1'), (-8, 1, 'Alpha-2'), (-7, 1, 'Alpha-2'),
(-6, -2, 'Bravo-1'), (-5, -2, 'Bravo-2'), (-4, -2, 'Bravo-3'),
(-3, -1, 'Charlie-1'), (-2, -1, 'Charlie-2'), (-1, -1, 'Charlie-3');
-- table to collect mapping Ids from @TempParents to @Parents
declare @ParentIdMaps table (ParentId int, TempParentId int)
-- merge data into @Parents table and collection of mapping Ids
merge into @Parents as target
using @TempParents as source on source.Id = target.Id
when matched then
update set Name = source.Name
when not matched then
insert (Name) values (Name)
output
inserted.Id, source.Id
into @ParentIdMaps
(ParentId, TempParentId);
-- merge data into @Children table and use of mapping Ids
merge into @Children as target
using
(
select
Id,
ParentId = m.ParentId,
Name
from
@TempChildren tc
inner join @ParentIdMaps m on m.TempParentId = tc.ParentId
)
as source on source.Id = target.Id
when matched then
update set ParentId = source.ParentId, Name = source.Name
when not matched then
insert (ParentId, Name) values (ParentId, Name)
when not matched by source and target.ParentId in (select Id from @TempParents) then
delete;
-- checking the result
-- see that 'Alfa' was renamed to 'Alpha'
-- and 'Delta' was deleted because it was not mentioned in @TempChildren
select
p.*,
c.*
from
@Parents p
inner join @Children c on c.ParentId = p.Id
order by
p.Id,
c.Id;
也许是触发器? – 2015-02-06 22:12:19
好的,如果你只有一条记录,那么你可以永远不要使用@@ identity ieven。如果有人将触发器插入带有标识的另一个表中,则可能返回错误的值。 – HLGEM 2015-02-06 22:12:24
'OUTPUT'子句可以与'INSERT','UPDATE','DELETE'和'MERGE'一起使用,并在'UPDATE'的情况下提供对值和值之前的访问。 – HABO 2015-02-07 01:18:11