检查我的数据库中是否存在文本C＃ [英] Check if text exist in my database C#

问题描述

嘿伙计们，任何人都可以帮我查一下数据库中是否有文字

这就是我现在写的内容

<

 connstring = SERVER = 188.121.43.9; PORT = 3306; DATABASE = mydbname; UID = mydbusername; PASSWORD = s1996;; 
 MySqlConnection conn = new MySqlConnection（connstring）; 
 MySqlCommand command = conn.CreateCommand（）; 
 command.CommandText =从dbtable中选择全部; 

>



这就是我的数据库的样子



<

 uname upass 
 test 1900 
 test2 1999 

>

i有textbox1

我想要的是

例如：

chek如果textbox1.text存在于列uname show MessageBox.Show（存在）



我尝试过：

嘿伙计们，任何人都可以帮我检查数据库中是否存在文本
这就是我现在写的内容
< 
 connstring =SERVER = 188.121.43.9; PORT = 3306; DATABASE = mydbname; UID = mydbusername; PASSWORD = s1996;; 
 MySqlConnection conn = new MySqlConnection（connstring）; 
 MySqlCommand command = conn.CreateCommand（）; 
 command.CommandText =从dbtable中选择全部; 
> 
 
这就是我的数据库看起来像
 
< 
 uname upass 
 test 1900 
 test2 1999 
> 
i有textbox1 
我想要的是
例如：
 chek如果textbox1.text存在于列uname上显示MessageBox.Show（exists）

解决方案

我会使用ExecuteScalar来提高效率......像这样：

  private   void  btnNext_Click（ object  sender，EventArgs e）
 {
  if （comboBox1.SelectedIndex == -1） return ; 
 使用（ var  conn =  new  SqlConnection（connstring））
 {
 conn.Open（）; 
  var  cmd =  new  SqlCommand 
 {
 CommandText =  从dbtable中选择count（*），其中UPPER（[name]）= @ name，
 Connection = conn 
}; 
 cmd.Parameters.AddWithValue（  @ name，comboBox1.SelectedItem.ToString（） ）; 
  var  res =（ int ）cmd.ExecuteScalar（）; 
  if （res >   0 ）
 MessageBox.Show（  exists）; 
} 
} 

注意事项：

- 我使用使用参见< a href =https://msdn.microsoft.com/en-us/library/ms254507(v=vs.110).aspx>建立连接 [ ^ ]

Quote：

当代码退出块时，Visual Basic或C＃中的Using块会自动处理连接，即使在未处理的异常情况下也是如此。

- 我使用了ExecuteScalar方法，因为它需要更少的代码和更少的资源 - 请参阅SqlCommand.ExecuteScalar Method（System.Data.SqlClient） [ ^ ]

- 我检查确保在尝试使用该值之前在comboBox上实际选择了某些内容。

< pre> String connstring = < span class =code-string>  SERVER = 188.121.43.9; PORT = 3306; DATABASE = mydbname; UID = mydbusername; PASSWORD = s1996;; 
 SqlConnection conn =  new  SqlConnection（connstring）; 
 SqlCommand command = conn.CreateCommand（）; 
 command.CommandText =  从dbtable中选择*其中name = @ name; 
 command.Parameters.AddWithValue（  @ name，comboBox1.SelectedValue）; 
 SqlDataAdapter sda =  new  SqlDataAdapter（cmd）; 
 DataTable dt =  new  DataTable（）; 
 sda.Fill（dt）; 
  if （dt.Rows.Count >   0 ）
 {
 MessageBox.Show（  exists）; 
} 

hey guys can anyone help me to check if a text exist in database
thats what im writting at this moment
<

connstring = "SERVER=188.121.43.9;PORT=3306;DATABASE=mydbname;UID=mydbusername;PASSWORD=s1996;";
        MySqlConnection conn = new MySqlConnection(connstring);
        MySqlCommand command = conn.CreateCommand();
        command.CommandText = "Select all from dbtable";

>

this is how my DB looks like

<

uname     upass
test      1900
test2     1999

>
i have textbox1
what i want is
for example :
chek if textbox1.text exist at column uname show MessageBox.Show("exist")

What I have tried:

hey guys can anyone help me to check if a text exist in database
thats what im writting at this moment
<
connstring = "SERVER=188.121.43.9;PORT=3306;DATABASE=mydbname;UID=mydbusername;PASSWORD=s1996;";
        MySqlConnection conn = new MySqlConnection(connstring);
        MySqlCommand command = conn.CreateCommand();
        command.CommandText = "Select all from dbtable";
>

this is how my DB looks like

<
uname     upass
test      1900
test2     1999
>
i have textbox1
what i want is
for example : 
chek if textbox1.text exist at column uname show MessageBox.Show("exist")

解决方案

I would use ExecuteScalar to be more efficient... like this:

private void btnNext_Click(object sender, EventArgs e)
{
    if (comboBox1.SelectedIndex == -1) return;
    using (var conn = new SqlConnection(connstring))
    {
        conn.Open();
        var cmd = new SqlCommand
        {
            CommandText = "select count(*) from dbtable where UPPER([name])=@name",
            Connection = conn
        };
        cmd.Parameters.AddWithValue("@name", comboBox1.SelectedItem.ToString());
        var res = (int)cmd.ExecuteScalar();
        if (res > 0) 
            MessageBox.Show("exist");
    }
}

Things to note:
- I've used using see Establishing the Connection[^]

Quote:

The Using block in Visual Basic or C# automatically disposes of the connection when the code exits the block, even in the case of an unhandled exception.

- I've used the ExecuteScalar method as it requires less code and fewer resources - see SqlCommand.ExecuteScalar Method (System.Data.SqlClient)[^]
- I check to ensure there is something actually selected on the comboBox before attempting to use the value.

<pre>String connstring = "SERVER=188.121.43.9;PORT=3306;DATABASE=mydbname;UID=mydbusername;PASSWORD=s1996;";
            SqlConnection conn = new SqlConnection(connstring);
            SqlCommand command = conn.CreateCommand();
            command.CommandText = "Select * from dbtable where name=@name";
            command.Parameters.AddWithValue("@name", comboBox1.SelectedValue);
            SqlDataAdapter sda = new SqlDataAdapter(cmd);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            if (dt.Rows.Count > 0)
            {
                MessageBox.Show("exist");
            }

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