Question

我正在搜索生成html表的查询。我找到了这个查询，但是我无法理解这里使用的这么多单引号是什么用的为什么所有代码都在变量中创建我是sql的新人请帮助我。

BEGIN
    SET NOCOUNT ON;

    IF @orderBy IS NULL
    BEGIN
        SET @orderBy = ''
    END

    SET @orderBy = REPLACE(@orderBy, '''', '''''');
    DECLARE @realQuery NVARCHAR(MAX) = ' //this is variable which take all query as string
    DECLARE @headerRow nvarchar(MAX);
    DECLARE @cols nvarchar(MAX);    

    SELECT * INTO #dynSql FROM (' + @query + ') sub; -- how this temp table create 

    SELECT @cols = COALESCE(@cols + '', '''''''', '', '''') + ''['' + name + ''] AS ''''td''''''
    FROM tempdb.sys.columns 
    WHERE object_id = object_id(''tempdb..#dynSql'')
    ORDER BY column_id;

    SET @cols = ''SET @html = CAST(( SELECT '' + @cols + '' FROM #dynSql ' + @orderBy + ' FOR XML PATH(''''tr''''), ELEMENTS XSINIL) AS nvarchar(max))''    

    EXEC sys.sp_executesql @cols, N''@html nvarchar(MAX) OUTPUT'', @html=@html OUTPUT
    --in coalesce why so many '''' used
    SELECT @headerRow = COALESCE(@headerRow + '''', '''') + ''<th>'' + name + ''</th>'' 
    FROM tempdb.sys.columns 
    WHERE object_id = object_id(''tempdb..#dynSql'')
    ORDER BY column_id;

    SET @headerRow = ''<tr>'' + @headerRow + ''</tr>'';

    SET @html = ''<table border="1">'' + @headerRow + @html + ''</table>'';    
';

    EXEC sys.sp_executesql @realQuery
    ,N'@html nvarchar(MAX) OUTPUT'
    ,@html = @html OUTPUT
END

以上查询工作正常，但我无法理解。

为什么在查询中使用如此多的单引号

0 个答案: