MAX(id) 使用 SqlDataReader C#
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MAX(id) using SqlDataReader C#
提问by Dan Kanze
How do I change this:
我如何改变这个：
using (SqlCommand myCommand = myConnection.CreateCommand())
{
myConnection.Open();
myCommand.CommandText = "SELECT FormID FROM tbl_Form";
using (SqlDataReader reader = myCommand.ExecuteReader())
{
while (reader.Read())
{
int FormID = reader.GetInt32(reader.GetOrdinal("FormID"));
MessageBox.Show(FormID.ToString());
}
}
}
to get MAX(FormID)?
获得MAX(FormID)？
My natural tendency is to throw a MAX around FormID but I'm getting an IndexOutOfRange exception.
我的自然倾向是在 FormID 周围抛出 MAX，但我收到 IndexOutOfRange 异常。
采纳答案by BrokenGlass
When you select the maximum id you shouldn't use a SqlDataReader- the query returns just one item, which by default is unnamed so your existing query breaks because it expects a result named "FormID" - although you could have "fixed" your query by using "SELECT MAX(FormID) as FormId FROM tbl_Form". Instead use ExecuteScalar():
当您选择最大 id 时，您不应使用 a SqlDataReader- 查询仅返回一项，默认情况下未命名，因此您现有的查询会中断，因为它需要名为“FormID”的结果 - 尽管您可以“修复”您的查询使用"SELECT MAX(FormID) as FormId FROM tbl_Form". 而是使用ExecuteScalar()：
myCommand.CommandText = "SELECT MAX(FormID) FROM tbl_Form";
int maxId = Convert.ToInt32(myCommand.ExecuteScalar());
回答by Antony Scott
It's been a while since I used this style of database access, but I think you just need
我已经有一段时间没有使用这种数据库访问方式了，但我认为您只需要
select max(FormID) from tbl_Form
along with a call to ExecuteScalar
以及对 ExecuteScalar 的调用
