C# 中的 SQL 更新语句

我有桌子“学生”

   P_ID   LastName  FirstName  Address  City

   1        Hansen    Ola                
   2        Svendson   Tove
   3        Petterson   Kari
   4        Nilsen       Johan
...and so on 

如何更改 C# 中的编辑代码

string firstName = "Ola";
string lastName ="Hansen";
string address = "ABC";
string city = "Salzburg";

string connectionString = System.Configuration.ConfigurationManager
                          .ConnectionStrings["LocalDB"].ConnectionString;
 
using (SqlConnection connection = new SqlConnection(connectionString))
using (SqlCommand command = connection.CreateCommand())
{ 
    command.CommandText = "INSERT INTO Student (LastName, FirstName, Address, City) 
                          VALUES (@ln, @fn, @add, @cit)";

    command.Parameters.AddWithValue("@ln", lastName);
    command.Parameters.AddWithValue("@fn", firstName);
    command.Parameters.AddWithValue("@add", address);
    command.Parameters.AddWithValue("@cit", city);

    connection.Open();
    command.ExecuteNonQuery();
    connection.Close();
} 
      

编辑条目的位置Lastname字段具有姓氏值并且名字段具有名字值。

我不想这样使用

 UPDATE Persons SET Address = 'Nissestien 67', City = 'Sandnes' 
 WHERE LastName = 'Tjessem' AND FirstName='Jakob'

我将原来的声明编辑为

 command.CommandText = "UPDATE Student(LastName, FirstName, Address, City) 
   VALUES (@ln, @fn, @add, @cit) WHERE LastName='" + lastName + 
                           "' AND FirstName='" +  firstName+"'";

但该声明并未得到执行。为什么会抛出SQL异常？有什么办法解决吗？

这不是在 SQL 中更新记录的正确方法：

command.CommandText = "UPDATE Student(LastName, FirstName, Address, City) VALUES (@ln, @fn, @add, @cit) WHERE LastName='" + lastName + "' AND FirstName='" + firstName+"'";

你应该这样写：

command.CommandText = "UPDATE Student 
SET Address = @add, City = @cit Where FirstName = @fn and LastName = @add";

然后添加与插入操作相同的参数。