数据类型text和varchar在等于运算符中不兼容 [英] The data types text and varchar are incompatible in the equal to operator

问题描述

我正在尝试访问数据库的数据网格视图上的所有记录，具体取决于通过具有2个分别用于user_name和password的文本框以及显示提交按钮记录的表单登录的用户的类型。但是我编写的代码给了我以下错误：数据类型text和varchar在equal运算符中不兼容。请提出更改建议。

I am trying to access all the records from database on a data grid view depending upon the type of user logging in through a form having 2 text-boxes for user_name and password respectively and on submit button records are displayed. But the code I have written is giving me the following error: The data types text and varchar are incompatible in the equal to operator. Please suggest changes.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Configuration;
using System.Data.SqlClient;


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

        private void Form1_Load(object sender, EventArgs e)
        {



        }

        private void button1_Click(object sender, EventArgs e)
        {

            string str = ConfigurationSettings.AppSettings["constring"].ToString();
            SqlConnection sqlcon = new SqlConnection(str);


            try
            {
                sqlcon.Open();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }


            SqlCommand sqlcmd = new SqlCommand("select user_type from employee where user_name='" + textBox1.Text + "'and pwd= '" + textBox2.Text + "' ;", sqlcon);


            SqlDataReader myReader = sqlcmd.ExecuteReader();

            string user_type=string.Empty;

            while(myReader.Read())
            {
            user_type= myReader["user_type"].ToString();
            }

            sqlcon.Close();



            sqlcon.Open();
            SqlCommand sqlcmd2 = new SqlCommand("select * from employee where user_type= '" +user_type + "'", sqlcon);
            SqlDataReader myReader2 = sqlcmd2.ExecuteReader();

          /*  SqlDataAdapter sqladapter = new SqlDataAdapter(sqlcmd2);
            DataSet ds = new DataSet();
            sqladapter.Fill(ds);
            dataGridView1.DataSource = ds.Tables[0];*/

            DataTable dt = new DataTable();
            dt.Columns.Add("ID", typeof(string));
            dt.Columns.Add("Name", typeof(string));
            dt.Columns.Add("Email_ID", typeof(string));
            dt.Columns.Add("Contact", typeof(string));
            dt.Columns.Add("Address", typeof(string));

            while (myReader2.Read())
            {
                DataRow dr = dt.NewRow();
                dr["ID"] = myReader2["ID"];
                dr["Name"] = myReader2["user_name"];
                dr["Email_ID"] = myReader2["Email_ID"];
                dr["Contact"] = myReader2["Contact"];
                dr["Address"] = myReader2["Address"];
                dt.Rows.Add(dr);
            }


            dataGridView1.DataSource = dt;


            sqlcon.Close();
        }

    }
}

推荐答案

这是一个简单的数据库问题。

This is a simple Database Problem.

在数据库生成脚本中进行了更改：

in the Database generation script change:

columnname text NULL,

至：

columnname varchar(number of chars) NULL,

在您的情况下，列名将为 user_name或 user_type

in your case columnname would be "user_name" or "user_type"

会出现此问题，因为SQL类型的文本为！与字符串比较不兼容！

this problem occurs, because SQL-Type text is !not compatible for comparison with strings!

将类型从文本更改为varchar（）后，操作便会正常工作

as soon as you change the type from text to varchar() the operation should work

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