第十四篇 SQL游标、函数的使用方法

游标的的使用有日常的开发和维护的过程不使用的并不多，但是碰到一些棘手的问题的时候，游标时常是个非常好的帮手，下面就说下游标的使用方法，方法自己以后查阅，和加深一些印象，下面以一个存储过程为例

 T-SQL中的游标定义在MSDN中如下:

DECLARE cursor_name CURSOR [ LOCAL | GLOBAL ]
     [ FORWARD_ONLY | SCROLL ]
     [ STATIC | KEYSET | DYNAMIC | FAST_FORWARD ]
     [ READ_ONLY | SCROLL_LOCKS | OPTIMISTIC ]
     [ TYPE_WARNING ]
     FOR select_statement
     [ FOR UPDATE [ OF column_name [ ,...n ] ] ]
[;]

ALTER PROCEDURE [dbo]. [XXXX]
    @ProcessName NVARCHAR (20) ---流程名
AS
    DECLARE @tempIncident INT
    DECLARE @tempCode NVARCHAR( 20)
    DECLARE @incident NVARCHAR( 100) ---实例号
    DECLARE @bicode NVARCHAR( 200)--- 单号
    DECLARE @taskCnt INT ---task为的数量
    DECLARE @flag INT
    DECLARE @bflag INT
    SET @flag = 0
    SET @bflag = 0

    ----定义一个游标--
    ----定义游标和定义一个变量是差不多的，不过后面要指定一个的查询语句，
    DECLARE mycur CURSOR
    FOR
        ( SELECT     bic. BI_Code ,----这时两个的数据是要使用的数据
                    bic.BI_Incident
          FROM    xxxxx AS inc ,
                    bic AS bic
          WHERE     inc .PROCESSNAME = bic .BI_ProcessName
                    AND INCIDENT = bic.BI_Incident
                    AND PROCESSNAME = @ProcessName
                    AND inc .STATUS = 2
                    AND ( bic. BI_AuditState = 4010
                          OR bic .BI_AuditState = 4040
                        )
        )
    OPEN mycur--打开这个游标

    FETCH NEXT FROM mycur INTO @tempCode, @tempIncident ---把值放到变量中
      --循环这个值
      --这是一个系统的取游标值的一个变量
    WHILE @@FETCH_STATUS = 0
        BEGIN
            SELECT  @taskCnt = COUNT(*)
            FROM    xxxxx
            WHERE   INCIDENT = @tempIncident
                    AND PROCESSNAME = @ProcessName
                    AND STATUS = 1

            IF @taskCnt > 0 ---有task=1 的数据则是可以自动处理的
                BEGIN
                    IF @flag = 0
                        BEGIN
                            SET @incident = CAST(@tempIncident AS NVARCHAR)
                        END
                    ELSE
                        SET @incident = @incident + ‘,‘
                            + CAST (@tempIncident AS NVARCHAR )
                    SET @flag = 1
                END

            ELSE
                BEGIN
                    IF @bflag = 0
                        SET @bicode = @tempCode
                    ELSE
                        SET @bicode = @bicode + ‘,‘ + @tempCode
                    SET @bflag = 1
                END
             ---这里的是把数据再次放到变量里面，以便循环的使用
            FETCH NEXT FROM mycur INTO @tempCode, @tempIncident
        END
    CLOSE mycur
    DEALLOCATE mycur
    IF @bicode IS NULL
        SET @bicode = ‘NULL‘
    IF @incident IS NULL
        SET @incident = ‘NULL‘
    ELSE
        UPDATE  xxxxx
        SET     STATUS = 1
        WHERE   PROCESSNAME = @ProcessName
                AND INCIDENT IN ( SELECT     value
                                  FROM      dbo .fn_Split( @incident, ‘,‘) )

SQL 函数的使用：

函数在SQL中的使用提高了SQL代码的重复利用，也方便我们更高效的去用SQL做更多的事：下面我就对标量的函数进行说明，其它的东西也基本上是大同小异.

1、标量函数

Create function 函数名（参数）

Returns 返回值数据类型

[with {Encryption | Schemabinding }]

[as]

begin

SQL语句(必须有return 变量或值)

例如：

ALTER FUNCTION [dbo]. [fn_Split](@sText varchar( 8000), @sDelim varchar(20 ) = ‘ ‘)
RETURNS @retArray TABLE (idx smallint Primary Key, value varchar(8000 ) COLLATE SQL_Latin1_General_CP1_CI_AS )

这样就是把一个函数的基本形式定义好了 如同在代码中写出 public string get(){}

后面的代码也就是日常的sql查询或者是一些的特殊的处理

ALTER   FUNCTION [dbo]. [fn_Split](@sText varchar( 8000), @sDelim varchar(20 ) = ‘ ‘)
 RETURNS @retArray TABLE (idx smallint Primary Key, value varchar(8000 ) COLLATE SQL_Latin1_General_CP1_CI_AS )
 AS
 BEGIN
 DECLARE @idx smallint ,
  @value varchar(8000 ),
  @bcontinue bit,
  @iStrike smallint,
  @iDelimlength tinyint

IF @sDelim = ‘Space‘
 BEGIN
 SET @sDelim = ‘ ‘
 END

SET @idx = 0
SET @sText = LTrim(RTrim (@sText))
SET @iDelimlength = DATALENGTH(@sDelim )
SET @bcontinue = 1

IF NOT ((@iDelimlength = 0 ) or (@sDelim = ‘Empty‘))
 BEGIN
 WHILE @bcontinue = 1
  BEGIN
  --If you can find the delimiter in the text, retrieve the first element and
   --insert it with its index into the return table.
    IF CHARINDEX (@sDelim, @sText)> 0
    BEGIN
    SET @value = SUBSTRING(@sText ,1, CHARINDEX( @sDelim,@sText )-1)
     BEGIN
     INSERT @retArray (idx , value )
     VALUES (@idx , @value )
     END

    --Trim the element and its delimiter from the front of the string.
    --Increment the index and loop.
    SET @iStrike = DATALENGTH(@value ) + @iDelimlength
    SET @idx = @idx + 1
    SET @sText = LTrim(Right(@sText ,DATALENGTH( @sText) - @iStrike ))

    END
   ELSE
    BEGIN
    --If you can’t find the delimiter in the text, @sText is the last value in
    --@retArray.
      SET @value = @sText
     BEGIN
     INSERT @retArray (idx , value )
     VALUES (@idx , @value )
     END
    --Exit the WHILE loop.
    SET @bcontinue = 0
    END
   END
  END
 ELSE
  BEGIN
  WHILE @bcontinue=1
   BEGIN
   --If the delimiter is an empty string, check for remaining text
   --instead of a delimiter. Insert the first character into the
   --retArray table. Trim the character from the front of the string.
   --Increment the index and loop.
   IF DATALENGTH(@sText )>1
    BEGIN
    SET @value = SUBSTRING(@sText ,1, 1)
     BEGIN
     INSERT @retArray (idx , value )
     VALUES (@idx , @value )
     END
    SET @idx = @idx+1
    SET @sText = SUBSTRING(@sText ,2, DATALENGTH(@sText )-1)

    END
   ELSE
    BEGIN
    --One character remains.
    --Insert the character, and exit the WHILE loop.
    INSERT @retArray (idx , value )
    VALUES (@idx , @sText )
    SET @bcontinue = 0
    END
  END

 END

 RETURN
 END