如何在 MS SQL 中插入标识列

Question

我有以下代码：

SqlCommand writeCommand = new SqlCommand("INSERT INTO computers(id)VALUES()", conn.GetConnection());
            writeCommand.ExecuteNonQuery();

表computers 包含一个名为id 的INT idientity(1,1) 列。

当我运行代码时，我得到一个System.Data.SqlClient.SqlException: Incorrect syntax near ')'。我试图找到解决方案，但在互联网上找不到。

Answer 1

如果该表还有其他列，并且您想用NULL 或其DEFAULT 值填充它们，那么您可以使用DEFAULT VALUES：

INSERT INTO dbo.computers
DEFAULT VALUES;

但是，如果您的表只有只有一列，那么亲自使用IDENTITY 是错误的选择；一张只有IDENTITY 的表显然被滥用了。相反，请使用SEQUENCE:

CREATE SEQUENCE dbo.Computers START WITH 1 INCREMENT BY 1;

这远更好地扩展，并且不会受到您可能遇到的竞争条件的影响。然后，在运行INSERT（或类似的）时，您将使用NEXT VALUE FOR dbo.Computers。

Answer 2

对于自动递增的标识列，数据库处理 id 值，除非我错过了您尝试执行的操作。

public void DemoInsert(string ComputerName, ref int newIdentifier)
{
    using (var conn = new SqlConnection { ConnectionString = ConnectionString })
    {
        using (var cmd = new SqlCommand { Connection = conn })
        {
            cmd.CommandText = "INSERT INTO computers (ComputerName) " + 
                              "VALUES (@ComputerName); " + 
                              "SELECT CAST(scope_identity() AS int);";

            cmd.Parameters.AddWithValue("@ComputerName", ComputerName);

            cn.Open();

            newIdentifier = (int)cmd.ExecuteScalar();
        }
    }
}

Answer 3

我有类似你的应用程序的代码，想想它是简单的 crud 应用程序

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        SqlConnection con;
        SqlDataAdapter da;
        SqlCommand cmd;
        DataSet ds;

        void fillGrid()
        {
            con = new SqlConnection("Data Source=.;Initial Catalog=schoolDb;Integrated Security=True");
            da = new SqlDataAdapter("Select * from ogrenciler",con);
            ds = new DataSet();
            con.Open();
            da.Fill(ds, "students");
            dataGridView1.DataSource = ds.Tables["students"];
            con.Close();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            fillGrid();
        }

        private void Addbtn_Click(object sender, EventArgs e)
        {
            cmd = new SqlCommand();
            con.Open();
            cmd.Connection = con;
            cmd.CommandText="insert into students(StudentId,StudentName,StudentSurname,City) values("+StudentId.Text+",'"+StudentName.Text+"','"+StudentSurname.Text+"','"+City.Text+"')";
            cmd.ExecuteNonQuery();
            con.Close();
            fillGrid();        

        }

        private void Updatebtn_Click(object sender, EventArgs e)
        {
            cmd = new SqlCommand();
            con.Open();
            cmd.Connection = con;
            cmd.CommandText = "update Students set ogrenci_ad='"+StudentName.Text+"',StudentName='"+StudentSurname.Text+"',City='"+City.Text+"' where StudentId="+StudentId.Text+"";
            cmd.ExecuteNonQuery();
            con.Close();
            fillGrid();
        }

        private void Deletebtn_Click(object sender, EventArgs e)
        {
            cmd = new SqlCommand();
            con.Open();
            cmd.Connection = con;
            cmd.CommandText = "delete from ogrenciler where ogrenci_no="+StudentId.Text+"";
            cmd.ExecuteNonQuery();
            con.Close();
            fillGrid();
        }
    }
}