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
以下是我的做法:
Select Identity(int, 1,1) AS PK, DatabaseID
Into #T
From @databases
Declare @maxPK int;Select @maxPK = MAX(PK) From #T
Declare @pk int;Set @pk = 1
While @pk <= @maxPK
Begin
-- Get one record
Select DatabaseID, Name, Server
From @databases
Where DatabaseID = (Select DatabaseID From #T Where PK = @pk)
--Do some processing here
--
Select @pk = @pk + 1
End
[编辑]因为我可能在第一次读这个问题时跳过了“变量”这个词,这里是一个更新的回答…
declare @databases table
(
PK int IDENTITY(1,1),
DatabaseID int,
Name varchar(15),
Server varchar(15)
)
-- insert a bunch rows into @databases
--/*
INSERT INTO @databases (DatabaseID, Name, Server) SELECT 1,'MainDB', 'MyServer'
INSERT INTO @databases (DatabaseID, Name, Server) SELECT 1,'MyDB', 'MyServer2'
--*/
Declare @maxPK int;Select @maxPK = MAX(PK) From @databases
Declare @pk int;Set @pk = 1
While @pk <= @maxPK
Begin
/* Get one record (you can read the values into some variables) */
Select DatabaseID, Name, Server
From @databases
Where PK = @pk
/* Do some processing here */
/* ... */
Select @pk = @pk + 1
End
其他回答
可以使用游标来做到这一点:
创建函数[dbo].f_teste_loop 返回@tabela表 ( 鳕鱼int, 省varchar (10) ) 作为 开始
insert into @tabela values (1, 'verde');
insert into @tabela values (2, 'amarelo');
insert into @tabela values (3, 'azul');
insert into @tabela values (4, 'branco');
return;
end
创建过程[dbo].[sp_test_loop] 作为 开始
DECLARE @cod int, @nome varchar(10);
DECLARE curLoop CURSOR STATIC LOCAL
FOR
SELECT
cod
,nome
FROM
dbo.f_teste_loop();
OPEN curLoop;
FETCH NEXT FROM curLoop
INTO @cod, @nome;
WHILE (@@FETCH_STATUS = 0)
BEGIN
PRINT @nome;
FETCH NEXT FROM curLoop
INTO @cod, @nome;
END
CLOSE curLoop;
DEALLOCATE curLoop;
end
简单说明一下,如果你使用的是SQL Server(2008及以上版本),下面的例子有:
While (Select Count(*) From #Temp) > 0
会不会更好
While EXISTS(SELECT * From #Temp)
Count将不得不触及表中的每一行,EXISTS只需要触及第一行。
这是我使用的2008 R2代码。我使用的这段代码是在所有故事的关键字段(SSNO & EMPR_NO)上构建索引
if object_ID('tempdb..#a')is not NULL drop table #a
select 'IF EXISTS (SELECT name FROM sysindexes WHERE name ='+CHAR(39)+''+'IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+char(39)+')'
+' begin DROP INDEX [IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+'] ON '+table_schema+'.'+table_name+' END Create index IDX_'+COLUMN_NAME+'_'+SUBSTRING(table_name,5,len(table_name)-3)+ ' on '+ table_schema+'.'+table_name+' ('+COLUMN_NAME+') ' 'Field'
,ROW_NUMBER() over (order by table_NAMe) as 'ROWNMBR'
into #a
from INFORMATION_SCHEMA.COLUMNS
where (COLUMN_NAME like '%_SSNO_%' or COLUMN_NAME like'%_EMPR_NO_')
and TABLE_SCHEMA='dbo'
declare @loopcntr int
declare @ROW int
declare @String nvarchar(1000)
set @loopcntr=(select count(*) from #a)
set @ROW=1
while (@ROW <= @loopcntr)
begin
select top 1 @String=a.Field
from #A a
where a.ROWNMBR = @ROW
execute sp_executesql @String
set @ROW = @ROW + 1
end
另一种不需要改变模式或使用临时表的方法:
DECLARE @rowCount int = 0
,@currentRow int = 1
,@databaseID int
,@name varchar(15)
,@server varchar(15);
SELECT @rowCount = COUNT(*)
FROM @databases;
WHILE (@currentRow <= @rowCount)
BEGIN
SELECT TOP 1
@databaseID = rt.[DatabaseID]
,@name = rt.[Name]
,@server = rt.[Server]
FROM (
SELECT ROW_NUMBER() OVER (
ORDER BY t.[DatabaseID], t.[Name], t.[Server]
) AS [RowNumber]
,t.[DatabaseID]
,t.[Name]
,t.[Server]
FROM @databases t
) rt
WHERE rt.[RowNumber] = @currentRow;
EXEC [your_stored_procedure] @databaseID, @name, @server;
SET @currentRow = @currentRow + 1;
END
SELECT @pk = @pk + 1
会更好:
SET @pk += @pk
避免使用SELECT如果你没有引用表,只是分配值。