在插入语句后从 SQL 数据库中检索自动增量 ID答案

【问题标题】：Retrieve Auto Increment ID from SQL Database after Insert Statement在插入语句后从 SQL 数据库中检索自动增量 ID
【发布时间】：2020-06-14 11:38:45
【问题描述】：

下面是我的代码，用于将数据插入数据库后检索自动增量 ID。

但是，在将数据插入数据库之前，我会获得自动增量 ID。

插入数据库后如何获取自增ID？

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {           
            RetrievePRReqID();
        }
    }

//获取ID方法

   private void RetrievePRReqID()
     {
        try
        {
            string query = "Select IDENT_CURRENT('tblPRRequest')";
            if (sqlCon.State == ConnectionState.Closed)
            {
                sqlCon.Open();

            }
            SqlCommand cmd = new SqlCommand(query, sqlCon);
            SqlDataReader reader = cmd.ExecuteReader();
            while(reader.Read())
            {
                int value = int.Parse(reader[0].ToString()) ;
                txt_PRNO.Text = value.ToString();
            }
        }
        catch(Exception)
        {
            throw;
        }
        finally
        {
            if(con.State == ConnectionState.Open)
            {
                con.Close();
            }
          }
        }

//请求按钮方法

     protected void btn_Request(object sender, EventArgs e)
    {
        string insertCmd = "INSERT INTO tblPRRequest (RequestTo,RequestFrom,RequestedByName) " +
            "VALUES (@RequestTo,@RequestFrom,@RequestedByName)";

        using (SqlConnection conn = new SqlConnection(cs))
        {
            conn.Open();
            using (SqlCommand sqlcmd = new SqlCommand(insertCmd, conn))
            {
                sqlcmd.Parameters.Clear();
                SqlCommand sqlCmd = new SqlCommand(insertCmd, sqlCon);
                sqlcmd.Parameters.AddWithValue("@RequestTo", lblPurchasingDept.Text);
                sqlcmd.Parameters.AddWithValue("@RequestFrom", ddlDept.SelectedItem.Text);
                sqlcmd.Parameters.AddWithValue("@RequestedByName", SUserName.Text);                   
                sqlcmd.ExecuteNonQuery();
            }
        }
        ***//After Insert into the table, I want to retrieve latest generated Auto Increment ID in here.***
      }

【问题讨论】：

标签： c# sql asp.net database auto-increment

【解决方案1】：

试试这个：

     protected void btn_Request(object sender, EventArgs e)
    {
        string insertCmd = "INSERT INTO tblPRRequest (RequestTo,RequestFrom,RequestedByName) " +
            "VALUES (@RequestTo,@RequestFrom,@RequestedByName)";

        using (SqlConnection conn = new SqlConnection(cs))
        {
            conn.Open();
            using (SqlCommand sqlcmd = new SqlCommand(insertCmd, conn))
            {
                sqlcmd.Parameters.Clear();
                SqlCommand sqlCmd = new SqlCommand(insertCmd, sqlCon);
                sqlcmd.Parameters.AddWithValue("@RequestTo", lblPurchasingDept.Text);
                sqlcmd.Parameters.AddWithValue("@RequestFrom", ddlDept.SelectedItem.Text);
                sqlcmd.Parameters.AddWithValue("@RequestedByName", SUserName.Text);
                sqlcmd.Parameters.Add("@ID", SqlDbType.Int).Direction = ParameterDirection.Output;                
                sqlcmd.ExecuteNonQuery();
            }
        }
        ***//After Insert into the table, I want to retrieve latest generated Auto Increment ID in here.***
        sqlcmd.Parameters["@ID"].value; // Access it like this
      }

如果您可以将ExecuteNonQuery 更改为ExecuteScalar，那就更简单了：What is the difference between ExecuteScalar, ExecuteReader and ExecuteNonQuery?

【讨论】：

【解决方案2】：

如 SQL Server 文档中所述 https://docs.microsoft.com/en-us/sql/t-sql/queries/output-clause-transact-sql?view=sql-server-ver15

OUTPUT 子句可能有助于在 INSERT 或 UPDATE 操作之后检索标识或计算列的值。

你必须改变你的 SQL 语句

INSERT INTO tblPRRequest (RequestTo,RequestFrom,RequestedByName)  
OUTOUT inserted.ID
-------^^^^^^^^_^^
VALUES (@RequestTo,@RequestFrom,@RequestedByName)

现在您可以使用 ExecuteScalar 来获取插入的值

 protected void btn_Request(object sender, EventArgs e)
 { 
    int id= 0;
    string insertCmd = "INSERT INTO tblPRRequest (RequestTo,RequestFrom,RequestedByName) " +
        "output inserted.ID" +
        "VALUES (@RequestTo,@RequestFrom,@RequestedByName)";

    using (SqlConnection conn = new SqlConnection(cs))
    {
        conn.Open();
        using (SqlCommand sqlcmd = new SqlCommand(insertCmd, conn))
        {
            sqlcmd.Parameters.AddWithValue("@RequestTo", lblPurchasingDept.Text);
            sqlcmd.Parameters.AddWithValue("@RequestFrom", ddlDept.SelectedItem.Text);
            sqlcmd.Parameters.AddWithValue("@RequestedByName", SUserName.Text);

            id = (int)sqlcmd.ExecuteScalar(); //the result is of Object type, cast it safely
        }
    }

    Debug.WriteLine(id.ToString()); // Access it like this
  }

【讨论】：

【解决方案3】：

通过参考@Mx.Wolf 的示例答案，我进行了一些修改以获得正确答案，下面是有效的代码：

     protected void btn_Request(object sender, EventArgs e)
    {
        object id ;
        string insertCmd = "INSERT INTO tblPRRequest (RequestTo,RequestFrom,RequestedByName) " +
            "output inserted.PRReqID " +
            "VALUES (@RequestTo,@RequestFrom,@RequestedByName)";

        using (SqlConnection conn = new SqlConnection(cs))
        {
            conn.Open();
            using (SqlCommand sqlcmd = new SqlCommand(insertCmd, conn))
            {
                sqlcmd.Parameters.AddWithValue("@RequestTo", lblPurchasingDept.Text);
                sqlcmd.Parameters.AddWithValue("@RequestFrom", ddlDept.SelectedItem.Text);
                sqlcmd.Parameters.AddWithValue("@RequestedByName", SUserName.Text);

                id = sqlcmd.ExecuteScalar(); //the result is of Object type, cast it safely
            }
        }

        Debug.WriteLine(id.ToString()); // Access it like this

【讨论】：