Question

我有一个attandence表，每天通过在当天添加新列来更改现在我希望看到月份的关注我不知道是否所有这些列都存在，如果通过添加完整的月份来选择所有列的查询

 BM_query = @"[" + st.m + "/1" + "/" + st.y + "] ," + "[" + st.m + "/2" + "/" + st.y + "] ," +
                           "[" + st.m + "/3" + "/" + st.y + "] ," + "[" + st.m + "/4" + "/" + st.y + "] ," +
                           "[" + st.m + "/5" + "/" + st.y + "] ," + "[" + st.m + "/6" + "/" + st.y + "] ," +
                           "[" + st.m + "/7" + "/" + st.y + "] ," + "[" + st.m + "/8" + "/" + st.y + "] ," +
                           "[" + st.m + "/9" + "/" + st.y + "] ," + "[" + st.m + "/10" + "/" + st.y + "] ," +
                           "[" + st.m + "/11" + "/" + st.y + "] ," + "[" + st.m + "/12" + "/" + st.y + "] ," +
                           "[" + st.m + "/13" + "/" + st.y + "] ," + "[" + st.m + "/14" + "/" + st.y + "] ," +
                           "[" + st.m + "/15" + "/" + st.y + "] ," + "[" + st.m + "/16" + "/" + st.y + "] ," +
                           "[" + st.m + "/17" + "/" + st.y + "] ," + "[" + st.m + "/18" + "/" + st.y + "] ," +
                           "[" + st.m + "/19" + "/" + st.y + "] ," + "[" + st.m + "/20" + "/" + st.y + "] ," +
                           "[" + st.m + "/21" + "/" + st.y + "] ," + "[" + st.m + "/22" + "/" + st.y + "] ," +
                           "[" + st.m + "/23" + "/" + st.y + "] ," + "[" + st.m + "/24" + "/" + st.y + "] ," +
                           "[" + st.m + "/25" + "/" + st.y + "] ," + "[" + st.m + "/26" + "/" + st.y + "] ," +
                           "[" + st.m + "/27" + "/" + st.y + "] ," + "[" + st.m + "/28" + "/" + st.y + "] ," +
                           "[" + st.m + "/29" + "/" + st.y + "] ," + "[" + st.m + "/30" + "/" + st.y + "] " ;



query = "select Roll_No , Student_Name, " + BM_query + " from [" + textBox2.Text + "_attandence] ";

如果列不存在，则显示无效的列名，如2/7/2017 ....等等我可以忽略这些不存在的列并继续下一个和下一个..

Answer 1

您可以使用如下查询检索表列的名称：

select COLUMN_NAME
from information_schema.columns
where table_name = 'attendance'

然后遍历结果以构建您的查询。

但是说真的，你应该回到这个的绘图板上。该表违背了RDBMS所代表的一切。当你达到表所允许的最大列数时你打算做什么？

当你只想看一个月的唱片时，你打算做什么？或者当您想要将两个日期之间的出勤加起来？您无法利用SQL中内置的任何功能。您需要通过构建字符串来构建所有查询，而您尝试执行的所有操作都将变得缓慢而脆弱。

Answer 2

如果您的数据表中填充了EVER扩展表中的数据，那么您可以检查列是否存在。

table.Columns.Contains("ColumnName");

Answer 3

这项工作很好，给出了所有存在的列名，忽略了其他

 DECLARE @dd INT;
 SET @dd = 1;

 DECLARE @tmp Varchar(5)
 SET @tmp = '';

 DECLARE @have Varchar(max)
 SET @have = '';

 WHILE @dd <= 31
 BEGIN 
 IF COL_LENGTH('test','2/' + CONVERT(varchar, @dd) + '/2017') IS NOT NULL
 set @have=@have+'2/' + CONVERT(varchar, @dd) + '/2017 ,';
    SET @dd = @dd + 1;

 END;

 PRINT @have;
 GO

Answer 4

使用以下查询

select COLUMN_NAME
from information_schema.columns
where table_name = 'your table name'

如果列存在，则从数据库中选择列

4 个答案: