SQLSERVER游标及循环语句

如果 SCROLL 选项未在 ISO 样式的 DECLARE CURSOR 语句中指定，则 NEXT 是唯一支持的 FETCH 选项。如果在 ISO 样式的 DECLARE CURSOR 语句中指定了 SCROLL 选项，则支持所有 FETCH 选项。

如果使用 Transact-SQL DECLARE 游标扩展插件，则应用下列规则：

• 如果指定了 FORWARD_ONLY 或 FAST_FORWARD，则 NEXT 是唯一受支持的 FETCH 选项。
• 如果未指定 DYNAMIC、FORWARD_ONLY 或 FAST_FORWARD 选项，并且指定了 KEYSET、STATIC 或 SCROLL 中的某一个，则支持所有 FETCH 选项。
• DYNAMIC SCROLL 游标支持除 ABSOLUTE 以外的所有 FETCH 选项。

@@FETCH_STATUS 函数报告上一个 FETCH 语句的状态。相同的信息记录在由 sp_describe_cursor 返回的游标中的 fetch_status 列中。这些状态信息应该用于在对由 FETCH 语句返回的数据进行任何操作之前，以确定这些数据的有效性。有关详细信息，请参阅 @@FETCH_STATUS (Transact-SQL)。

FETCH 权限默认授予任何有效的用户。

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A. 在简单的游标中使用 FETCH

以下示例为 Person.Contact 表中姓氏以字母 B 开头的行声明了一个简单的游标，并使用 FETCH NEXT 逐个提取这些行。FETCH 语句以单行结果集形式返回在 DECLARE CURSOR 中指定的列的值。

USE AdventureWorks
GO
DECLARE contact_cursor CURSOR FOR
SELECT LastName FROM Person.Contact
WHERE LastName LIKE 'B%'
ORDER BY LastName

OPEN contact_cursor

-- Perform the first fetch.
FETCH NEXT FROM contact_cursor

-- Check @@FETCH_STATUS to see if there are any more rows to fetch.
WHILE @@FETCH_STATUS = 0
BEGIN
   -- This is executed as long as the previous fetch succeeds.
   FETCH NEXT FROM contact_cursor
END

CLOSE contact_cursor
DEALLOCATE contact_cursor
GO

B. 使用 FETCH 将值存入变量

以下示例与示例 A 相似，但 FETCH 语句的输出存储于局部变量而不是直接返回到客户端。PRINT 语句将变量组合成单一字符串并将其返回到客户端。

USE AdventureWorks
GO
-- Declare the variables to store the values returned by FETCH.
DECLARE @LastName varchar(50),@FirstName varchar(50)

DECLARE contact_cursor CURSOR FOR
SELECT LastName,FirstName FROM Person.Contact
WHERE LastName LIKE 'B%'
ORDER BY LastName,FirstName

OPEN contact_cursor

-- Perform the first fetch and store the values in variables.
-- Note: The variables are in the same order as the columns
-- in the SELECT statement. 

FETCH NEXT FROM contact_cursor
INTO @LastName,@FirstName

-- Check @@FETCH_STATUS to see if there are any more rows to fetch.
WHILE @@FETCH_STATUS = 0
BEGIN

   -- Concatenate and display the current values in the variables.
   PRINT 'Contact Name: ' + @FirstName + ' ' +  @LastName

   -- This is executed as long as the previous fetch succeeds.
   FETCH NEXT FROM contact_cursor
   INTO @LastName,@FirstName
END

CLOSE contact_cursor
DEALLOCATE contact_cursor
GO

C. 声明 SCROLL 游标并使用其他 FETCH 选项

以下示例创建一个 SCROLL 游标，使其通过 LAST、PRIOR、RELATIVE 和 ABSOLUTE 选项支持全部滚动功能。

。

简单的FOR循环等：

declare ? @i ? int ?
? set ? @i=0 ?
? while ? @i<10 ?
? begin ?
? ? ? set ? @i ? = ? @i+1 ?
? end ?
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? SQL ? SERVER不支持FOR循环

USE AdventureWorks
GO
-- Execute the SELECT statement alone to show the 
-- full result set that is used by the cursor.
SELECT LastName,FirstName FROM Person.Contact
ORDER BY LastName,FirstName

-- Declare the cursor.
DECLARE contact_cursor SCROLL CURSOR FOR
SELECT LastName,FirstName

OPEN contact_cursor

-- Fetch the last row in the cursor.
FETCH LAST FROM contact_cursor

-- Fetch the row immediately prior to the current row in the cursor.
FETCH PRIOR FROM contact_cursor

-- Fetch the second row in the cursor.
FETCH ABSOLUTE 2 FROM contact_cursor

-- Fetch the row that is three rows after the current row.
FETCH RELATIVE 3 FROM contact_cursor

-- Fetch the row that is two rows prior to the current row.
FETCH RELATIVE -2 FROM contact_cursor

CLOSE contact_cursor
DEALLOCATE contact_cursor
GO

FETCH 
??????????[ [ NEXT | PRIOR | FIRST | LAST 
????????????????????| ABSOLUTE { n | @nvar } 
????????????????????| RELATIVE { n | @nvar } 
???????????????] 
???????????????FROM 
??????????] 
{ { [ GLOBAL ] cursor_name } | @cursor_variable_name } 
[ INTO @variable_name [,...n ] ]