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重构sql server的sys.helptext存储的例子

时间:2016-09-23 00:00:00 编辑:简简单单 来源:转载

1、sys.helptext存储的功能和效果
 
近来在研究sql server提供的现实可编程对象定义体的方法包括:sys.syscomments(视图)、sys.all_sql_modules(sys.sql_modules)(视图)、object_definition(函数)和sys.helptext(存储)。针对以上方式的不同以后有时间在写成博文。本文主要研究了sys.helptext的显示效果,感觉有些不太美好。先看该存储的现实效果如下图:

重构sql server的sys.helptext存储的例子


上图现在看没有什么的,那就将如下图的Text字段列内容复制放入单独的文件中再看其效果如下图:

 

重构sql server的sys.helptext存储的例子


上图我红色矩形框标注的地方了吧,每个行后都增加了char(13)和char(10)这两个字符导致的这样的显示效果,如果按照这个结果为基础进行变更,就增加了可编程对象定义的长度(主要是char(13)和char(10))。
 
2、重构sys.helptext存储(命名为dbo.usp_helptext)提供直观的效果
 
发现了sys.helptext的显示效果,我自己感觉不太满意,那么就重构嘛。重构后的代码如下:
 
if object_id(N'dbo.usp_helptext', 'P') IS NOT NULL
begin
    drop procedure [dbo].[usp_helptext];
end
go
 
create procedure [dbo].[usp_helptext]
(
     @objname nvarchar(776)
    ,@columnname sysname = NULL
    ,@keeporiginal bit = NULL
)
as
begin
    set nocount on
 
    set @keeporiginal = ISNULL(@keeporiginal, 1);   
 
    declare @dbname sysname
    ,@objid    int
    ,@BlankSpaceAdded   int
    ,@BasePos       int
    ,@CurrentPos    int
    ,@TextLength    int
    ,@LineId        int
    ,@AddOnLen      int
    ,@LFCR          int --lengths of line feed carriage return
    ,@DefinedLength int
 
    /* NOTE: Length of @SyscomText is 4000 to replace the length of
    ** text column in syscomments.
    ** lengths on @Line, #CommentText Text column and
    ** value for @DefinedLength are all 255. These need to all have
    ** the same values. 255 was selected in order for the max length
    ** display using down level clients
    */
    ,@SyscomText    nvarchar(4000)
    ,@Line          nvarchar(255)
 
    select @DefinedLength = 255
    select @BlankSpaceAdded = 0 /*Keeps track of blank spaces at end of lines. Note Len function ignores
                                    trailing blank spaces*/
    CREATE TABLE #CommentText
    (LineId    int
        ,Text  nvarchar(255) collate catalog_default)
 
    /*
    **  Make sure the @objname is local to the current database.
    */
    select @dbname = parsename(@objname,3)
    if @dbname is null
        select @dbname = db_name()
    else if @dbname <> db_name()
            begin
                    raiserror(15250,-1,-1)
                    return (1)
            end
 
    /*
    **  See if @objname exists.
    */
    select @objid = object_id(@objname)
    if (@objid is null)
            begin
            raiserror(15009,-1,-1,@objname,@dbname)
            return (1)
            end
 
    -- If second parameter was given.
    if ( @columnname is not null)
        begin
            -- Check if it is a table
            if (select count(*) from sys.objects where object_id = @objid and type in ('S ','U ','TF'))=0
                begin
                    raiserror(15218,-1,-1,@objname)
                    return(1)
                end
            -- check if it is a correct column name
            if ((select 'count'=count(*) from sys.columns where name = @columnname and object_id = @objid) =0)
                begin
                    raiserror(15645,-1,-1,@columnname)
                    return(1)
                end
        if (ColumnProperty(@objid, @columnname, 'IsComputed') = 0)
            begin
                raiserror(15646,-1,-1,@columnname)
                return(1)
            end
 
            declare ms_crs_syscom  CURSOR LOCAL
            FOR select text from syscomments where id = @objid and encrypted = 0 and number =
                            (select column_id from sys.columns where name = @columnname and object_id = @objid)
                            order by number,colid
            FOR READ ONLY
 
        end
    else if @objid < 0    -- Handle system-objects
        begin
            -- Check count of rows with text data
            if (select count(*) from master.sys.syscomments where id = @objid and text is not null) = 0
                begin
                    raiserror(15197,-1,-1,@objname)
                    return (1)
                end
 
            declare ms_crs_syscom CURSOR LOCAL FOR select text from master.sys.syscomments where id = @objid
                ORDER BY number, colid FOR READ ONLY
        end
    else
        begin
            /*
            **  Find out how many lines of text are coming back,
            **  and return if there are none.
            */
            if (select count(*) from syscomments c, sysobjects o where o.xtype not in ('S', 'U')
                and o.id = c.id and o.id = @objid) = 0
                    begin
                            raiserror(15197,-1,-1,@objname)
                            return (1)
                    end
 
            if (select count(*) from syscomments where id = @objid and encrypted = 0) = 0
                    begin
                            raiserror(15471,-1,-1,@objname)
                            return (0)
                    end
 
            declare ms_crs_syscom  CURSOR LOCAL
            FOR select text from syscomments where id = @objid and encrypted = 0
                    ORDER BY number, colid
            FOR READ ONLY
 
        end
 
    /*
    **  else get the text.
    */
    select @LFCR = 2
    select @LineId = 1
 
    open ms_crs_syscom
 
    fetch next from ms_crs_syscom into @SyscomText
 
    while @@fetch_status >= 0
    begin
        select  @BasePos    = 1
        select  @CurrentPos = 1
        select  @TextLength = LEN(@SyscomText)
 
        while @CurrentPos  != 0
        begin
            --Looking for end of line followed by carriage return
            select @CurrentPos =   CHARINDEX(char(13)+char(10), @SyscomText, @BasePos)
 
            --If carriage return found
            IF @CurrentPos != 0
            begin
                /*If new value for @Lines length will be > then the
                **set length then insert current contents of @line
                **and proceed.
                */
                while (isnull(LEN(@Line),0) + @BlankSpaceAdded + @CurrentPos-@BasePos + @LFCR) > @DefinedLength
                begin
                    select @AddOnLen = @DefinedLength-(isnull(LEN(@Line),0) + @BlankSpaceAdded)
                    insert #CommentText values
                    ( @LineId,
                        isnull(@Line, N'') + isnull(SUBSTRING(@SyscomText, @BasePos, @AddOnLen), N''))
                    select @Line = NULL, @LineId = @LineId + 1,
                            @BasePos = @BasePos + @AddOnLen, @BlankSpaceAdded = 0
                end
 
                -- 注释系统原来的使用如下修改
                --select @Line    = isnull(@Line, N'') + isnull(SUBSTRING(@SyscomText, @BasePos, @CurrentPos-@BasePos + @LFCR), N'')
                select @Line    = isnull(@Line, N'') + isnull(SUBSTRING(@SyscomText, @BasePos, @CurrentPos-@BasePos + (CASE @keeporiginal WHEN 1 THEN @LFCR ELSE 0 END)), N'')
                select @BasePos = @CurrentPos+2
                insert #CommentText values( @LineId, @Line )
                select @LineId = @LineId + 1
                select @Line = NULL
            end
            else
            --else carriage return not found
            begin
                IF @BasePos <= @TextLength
                begin
                    /*If new value for @Lines length will be > then the
                    **defined length
                    */
                    while (isnull(LEN(@Line),0) + @BlankSpaceAdded + @TextLength-@BasePos+1 ) > @DefinedLength
                    begin
                        select @AddOnLen = @DefinedLength - (isnull(LEN(@Line),0) + @BlankSpaceAdded)
                        INSERT #CommentText VALUES
                        ( @LineId,
                            isnull(@Line, N'') + isnull(SUBSTRING(@SyscomText, @BasePos, @AddOnLen), N''))
                        select @Line = NULL, @LineId = @LineId + 1,
                            @BasePos = @BasePos + @AddOnLen, @BlankSpaceAdded = 0
                    end
                    select @Line = isnull(@Line, N'') + isnull(SUBSTRING(@SyscomText, @BasePos, @TextLength-@BasePos+1 ), N'')
                    if LEN(@Line) < @DefinedLength and charindex(' ', @SyscomText, @TextLength+1 ) > 0
                    begin
                        select @Line = @Line + ' ', @BlankSpaceAdded = 1
                    end
                end
            end
        end
 
        FETCH NEXT from ms_crs_syscom into @SyscomText
    end
 
    IF @Line is NOT NULL
        INSERT #CommentText VALUES( @LineId, @Line )
 
    select Text from #CommentText order by LineId
 
    CLOSE  ms_crs_syscom
    DEALLOCATE     ms_crs_syscom
 
    DROP TABLE     #CommentText   
 
    return (0) -- sp_helptext
end
go
 

以上修改之处我已经标注了,其他的均来源sys.helptext内容。
那就看看重构后的效果,如下图:

重构sql server的sys.helptext存储的例子


以上显示并看不出和sys.helptext的有何不同,继续讲Text内容复制放入单独为文件中效果如下图:

重构sql server的sys.helptext存储的例子


上图红色矩形框就是显示的效果,下部分是为了对比,这部分可以使用如下代码显示器效果:
EXEC [sys].[sp_helptext]
     @objname = N'sys.fn_get_sql'    -- nvarchar(776)
    ,@columnname = NULL -- sysname
GO
 
EXEC [dbo].[usp_helptext]
     @objname = N'sys.fn_get_sql'    -- nvarchar(776)
    ,@columnname = NULL -- sysname
    ,@keeporiginal = 1 -- bit
GO
 

 
注意:dbo.usp_helptext兼容了sys.helptext的功能。
 
3、sys.helptext和dbo.usp_helptext的限制以及解决方案
 
查阅了sys.helptext的源码和其对应的联机帮助文档,发现其输出的字段列Text每行最多255个双字节字符,其输出到客户端最终的大小是4000个双字节字符,这个可以通过编码程序(例如VS程序读取获取等)突破这个限制。
 
其最大的缺点是每行255个,有可能遇到一行中一个分隔符前一部分属于前一个255个双字节字符,后一部分属于后一个255双字节字符的前部分。
具体的测试代码如下:
IF OBJECT_ID(N'[dbo].[uvm_MyTestView]', 'V') IS NOT NULL
BEGIN
    DROP VIEW [dbo].[uvm_MyTestView];
END
GO   
 
CREATE VIEW [dbo].[uvm_MyTestView]
AS
    SELECT
          1 AS N'Col_1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111', 2 AS [Col_2222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222222]
GO
 
 

效果展示如下图:


上图显示的效果就是出现了截断。消除这个限制那就使用函数object_definition(不过这个也有缺点的,以后才单独讲解输出可编程对象定义的内容的区别)。
 
4、总结语
 
学习sql server提供的系统对象,发现他们写的代码真的很严密的,很多规范以及异常处理等,确实学到了很多的,不过也发现有些sql server的内部限制是不写出来的,如表记录行最大8060字节的限制以及可边长长度溢出到row-overflow索引分配类型的数据页后也在原来的记录行中增加24字节的指针这样也可有能超过行最大8060字节的限制。可能我看理论太少的缘故吧。唯有继续精进,代码编程还是要继续的,有时候sql server客户端输出的最大4000个双字节字符的限制可以通过编程的方式得到完本的解决。
 
昨天看到园中的一篇博文print、sp_helptext的限制与扩展通过PRINT输出分批次打印超长的字符串,也会遇到某个标识符截断的问题,因为PRINT每次到打印到客户端总增加了char(13)和char(10)这两个字符,这样就可能将一个标识符分割为前后两个批次。

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