尝试访问数据库C＃asp.net时“源”附近的语法错误

Question

string databaseLocation = "|DataDirectory|\\Users.mdf";
string connectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=" + databaseLocation + ";Integrated Security=True;User Instance=True";    
SqlConnection sqlConnection = new SqlConnection(connectionString);
SqlCommand command = new SqlCommand();
command.CommandText = String.Format("SELECT * FROM Users WHERE Username = {0}", username);
command.CommandType = CommandType.Text;
command.Connection = sqlConnection;
sqlConnection.Open();
int numberOfRows = command.ExecuteNonQuery();
sqlConnection.Close();
return numberOfRows;

这应该检查Users.mdf数据库中用户名的出现次数。 但是当我击中ExecuteNonQuery时，我收到“源附近的语法错误”运行时错误。 我找不到任何错误...请帮助:)

Answer 1

您格式化的sql语句不包含用户名的分隔符：

command.CommandText = String.Format("SELECT * FROM Users WHERE Username = {0}", username);

将命令文本设置为：

SELECT * FROM Users WHERE Username = foo

这很容易纠正，但是最好使用SqlParameter ：

command.CommandText = "SELECT * FROM Users WHERE Username = @username");
command.Parameters.AddWithValue("@username", username);

---

另外，由于select不影响行，因此ExecuteNonQuery将为受影响的行数返回-1。 而是：

command.CommandText = "SELECT COUNT(*) FROM Users WHERE Username = @username");
command.Parameters.AddWithValue("@username", username);
...
int numberOfRows = (int)command.ExecuteScalar();

Answer 2

您的代码应为：

string databaseLocation = "|DataDirectory|\\Users.mdf";
string connectionString = "Data Source=.\\SQLEXPRESS;AttachDbFilename=" + databaseLocation + ";Integrated Security=True;User Instance=True";    
SqlConnection sqlConnection = new SqlConnection(connectionString);
SqlCommand command = new SqlCommand();
command.CommandText = "SELECT COUNT(*) FROM Users WHERE Username = @User";
command.CommandType = CommandType.Text;
command.Parameters.AddWithValue("@User",username);
command.Connection = sqlConnection;
sqlConnection.Open();
int numberOfRows = command.ExecuteScalar();
sqlConnection.Close();
return numberOfRows;