假设我有以下简单的表变量:
declare @databases table
(
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into @databases
如果我想遍历各行,声明和使用游标是我唯一的选择吗?还有别的办法吗?
假设我有以下简单的表变量:
declare @databases table
(
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into @databases
如果我想遍历各行,声明和使用游标是我唯一的选择吗?还有别的办法吗?
当前回答
如果您别无选择,只能逐行创建FAST_FORWARD游标。它和构建while循环一样快,而且更容易长期维护。
FAST_FORWARD 指定一个启用性能优化的FORWARD_ONLY、READ_ONLY游标。如果还指定了SCROLL或FOR_UPDATE,则FAST_FORWARD不能指定。
其他回答
我同意之前的帖子,基于集的操作通常会执行得更好,但如果你确实需要遍历行,下面是我将采取的方法:
Add a new field to your table variable (Data Type Bit, default 0) Insert your data Select the Top 1 Row where fUsed = 0 (Note: fUsed is the name of the field in step 1) Perform whatever processing you need to do Update the record in your table variable by setting fUsed = 1 for the record Select the next unused record from the table and repeat the process DECLARE @databases TABLE ( DatabaseID int, Name varchar(15), Server varchar(15), fUsed BIT DEFAULT 0 ) -- insert a bunch rows into @databases DECLARE @DBID INT SELECT TOP 1 @DBID = DatabaseID from @databases where fUsed = 0 WHILE @@ROWCOUNT <> 0 and @DBID IS NOT NULL BEGIN -- Perform your processing here --Update the record to "used" UPDATE @databases SET fUsed = 1 WHERE DatabaseID = @DBID --Get the next record SELECT TOP 1 @DBID = DatabaseID from @databases where fUsed = 0 END
下面是我的解决方案,它使用了一个无限循环、BREAK语句和@@ROWCOUNT函数。没有游标或临时表是必要的,我只需要写一个查询,以获得下一行在@databases表:
declare @databases table
(
DatabaseID int,
[Name] varchar(15),
[Server] varchar(15)
);
-- Populate the [@databases] table with test data.
insert into @databases (DatabaseID, [Name], [Server])
select X.DatabaseID, X.[Name], X.[Server]
from (values
(1, 'Roger', 'ServerA'),
(5, 'Suzy', 'ServerB'),
(8675309, 'Jenny', 'TommyTutone')
) X (DatabaseID, [Name], [Server])
-- Create an infinite loop & ensure that a break condition is reached in the loop code.
declare @databaseId int;
while (1=1)
begin
-- Get the next database ID.
select top(1) @databaseId = DatabaseId
from @databases
where DatabaseId > isnull(@databaseId, 0);
-- If no rows were found by the preceding SQL query, you're done; exit the WHILE loop.
if (@@ROWCOUNT = 0) break;
-- Otherwise, do whatever you need to do with the current [@databases] table row here.
print 'Processing @databaseId #' + cast(@databaseId as varchar(50));
end
像这样定义临时表-
declare @databases table
(
RowID int not null identity(1,1) primary key,
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into @databases
然后这样做——
declare @i int
select @i = min(RowID) from @databases
declare @max int
select @max = max(RowID) from @databases
while @i <= @max begin
select DatabaseID, Name, Server from @database where RowID = @i --do some stuff
set @i = @i + 1
end
轻量级,不需要创建额外的表,如果您在表上有一个整数ID
Declare @id int = 0, @anything nvarchar(max)
WHILE(1=1) BEGIN
Select Top 1 @anything=[Anything],@id=@id+1 FROM Table WHERE ID>@id
if(@@ROWCOUNT=0) break;
--Process @anything
END
如果您别无选择,只能逐行创建FAST_FORWARD游标。它和构建while循环一样快,而且更容易长期维护。
FAST_FORWARD 指定一个启用性能优化的FORWARD_ONLY、READ_ONLY游标。如果还指定了SCROLL或FOR_UPDATE,则FAST_FORWARD不能指定。