SQL查询和asp.net

Question

你好朋友以下是我的查询其中displaylist是对象如果stringBuilder有零长度有时，但在这种情况下，它给出错误附近FROM语法不正确，所以我如何避免这个问题我需要写一个在其他如果形式来避免这个或请建议我做一个最好的解决方案，也从来看

string cmd = @"SELECT [tbl_course].course_name as Course_Name , [tbl_branch].branch_name as Branch_Name,"+displayList+@" FROM [tbl_students], [tbl_course], [tbl_branch] 
         WHERE [tbl_students].course_id= @courseId 
         AND [tbl_students].branch_id IN(" + branchId + @") 
         AND (@firstYrPercent is null OR[tbl_students].first_year_percent>=@firstYrPercent) 
         AND (@secondYrpercent is null OR[tbl_students].second_year_percent>=@secondYrPercent) 
         AND (@thirdYrPercent is null OR[tbl_students].third_year_percent>=@thirdYrPercent) 
         AND (@finalYearpercent is null OR[tbl_students].final_year_percent>=@finalYearpercent) 
         AND (@currentDegeePercentage is null OR[tbl_students].current_degree_percent>=@currentDegeePercentage) 
         AND (@passoutYear is null OR[tbl_students].passing_year>=@passoutYear) 
         AND (@currentBacklog is null OR[tbl_students].current_backlog<=@currentBacklog) 
         AND [tbl_students].gender=@sex 
         AND (@eGap is null OR [tbl_students].gapin_education<=@eGap) 
         AND (@highSchoolPercentge is null OR[tbl_students].highschool_percentage>=@highSchoolPercentge) 
         AND (@higherSchoolPercentage is null OR[tbl_students].ssc_percentage>=@higherSchoolPercentage) 
         AND (@grauationPercentage is null OR[tbl_students].graduation_percentage>=@grauationPercentage) 
         AND (@diplomaPercentage is null OR[tbl_students].diploma_percentage>=@diplomaPercentage) 
         AND (@noOfAtkt is null OR[tbl_students].number_of_ATKT<=@noOfAtkt) 
         AND (@validDate is null OR[tbl_students].DOB<=@validDate) 
         AND [tbl_students].branch_i 

d=[tbl_branch].branch_id AND [tbl_students].course_id=[tbl_course].course_id"; 

Answer 1

问题是你插入显示列表的价值就在接近逗号效率和性能点不同的查询。如果显示列表是空的，那么你的SQL语句如下所示：

...[tbl_branch].branch_name as Branch_Name, FROM [tbl_students]... 

因此，无论包括dispalyList（displayList = ", [tbl_branch].branch_foo"）逗号或使用条件语句，将其插入SQL时：

string cmd = @"SELECT [tbl_course].course_name as Course_Name , [tbl_branch].branch_name as Branch_Name" + String.IsNullOrEmpty(displayList) ? "" : ", " + displayList + @" FROM [tbl_students]...";