c# - 数据类型 text 和 varchar 在 C# 中的等于运算符中不兼容

Question

我正在尝试从 employeeTable 访问数据 empname，但我编写的代码出现以下错误:

The data types text and varchar are incompatible in the equal to operator.

请提出解决方案

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    string Connection = "Data Source=(local);Initial catalog=Test;Integrated Security=true";
    string Query = "SELECT * FROM  EmployeeTable WHERE empname='" + comboBox1.Text + "' ;";

    SqlConnection conn = new SqlConnection(Connection);
    SqlCommand cmd = new SqlCommand(Query, conn);

    conn.Open();
    SqlDataReader reader = cmd.ExecuteReader();

    while (reader.Read())     
    {
        textBoxEmpName.Text = reader["EmpName"].ToString();
    }
}

Answer 1

您不能将 text 与 varchar 进行比较，但作为对将来遇到此问题的任何人的回答，只需将 text 列转换为 varchar 以进行查询。

SELECT * FROM  EmployeeTable WHERE CONVERT(VARCHAR, empname) = '" + comboBox1.Text + "' ;";

始终使用 parameters

SELECT * FROM  EmployeeTable WHERE CONVERT(VARCHAR, empname) = @comboBox";