How to subtract quantity from parent table and put that amount into child table in c# forms

Question

Hello guys I'm a student on 3th year of IT and I've found so much help from this forum, I am stuck with my project creating program in C# so I need your help I have 2 tables in my Data Base :

Materials Table wich has : idmaterial(INT) , name_material(VARCHAR), quantity_material(FLOAT), mesuring_unit(VARCHAR), code_material(INT)

Scraps Table (Scraps from Material) wich has : idscrap(INT), Materials_idmaterial(INT) .

They are connected with Non-Identifying Relation 1:1. Now I have a Combo Box in my C# Form presented down below. I need to take from table Materials (name_material , quantity_material , mesuring_unit , code_material) and subtract the quantity that I insert in the textBox on my Form. For example I have 120 kg of wool in my Material table and I want to put 2 kg to scrap table , how do I do it in C# ...
Pictures :

https://prnt.sc/hdvGuXJWNI0Q - My Diagram in mysql (It is on my language but I translated every cell name for you guys)
https://prnt.sc/lgIRVTCOe670 - Materials Panel
https://prnt.sc/t1IGxpgJ8GHl - Choosing material via combo box in scraps panel
https://prnt.sc/6InfCPpezZga - Example on how I want to subtract

Answer 1

@Studnet_1999 , based on your description, I almost understand your requirement about your questions.

Here is a code example you could refer to.

public partial class Form1 : Form  
{  
    public Form1()  
    {  
        InitializeComponent();  
    }  
    static string connstr = "str";  
    SqlConnection connection=new SqlConnection(connstr);  

    private void Form1_Load(object sender, EventArgs e)  
    {  
        loaddata();  
        connection.Open();  
        string sql = "select *from Materials";  
        SqlCommand sqlCommand = new SqlCommand(sql, connection);  
        SqlDataReader reader = sqlCommand.ExecuteReader();  
        while (reader.Read())  
        {  
            comboBox1.Items.Add(reader["name_material"].ToString());  

        }  
        connection.Close();  
        comboBox1.SelectedIndexChanged += ComboBox1_SelectedIndexChanged;  
    }  

    private void ComboBox1_SelectedIndexChanged(object sender, EventArgs e)  
    {  
        string value=comboBox1.SelectedItem.ToString();  
        connection.Open();  
        string sql =string.Format("select idmaterial from Materials where name_material='{0}'",value);  

        SqlCommand sqlCommand = new SqlCommand(sql, connection);  
        int idmaterial =(int) sqlCommand.ExecuteScalar();  
        sql = string.Format("select idscrap,Materials_idmaterial from Scraps where Materials_idmaterial={0}", idmaterial);  
        SqlDataAdapter adapter = new SqlDataAdapter(sql,connection);  
        DataSet ds = new DataSet();  
        adapter.Fill(ds);  
        dataGridView2.DataSource= ds.Tables[0];  
        connection.Close();  

    }  

    private void tabControl1_Click(object sender, EventArgs e)  
    {  
        if(tabControl1.SelectedTab.Name== "tabPage1")  
        {  
            loaddata();  
        }  
        if(tabControl1.SelectedTab.Name == "tabPage2")  
        {  
            textBox1.Clear();  
            comboBox1.Text = "";  
        }  
        

    }  


    public void loaddata()  
    {  
        connection.Open();  
        string sql = "select *from Materials";  
        DataSet ds = new DataSet();  
        SqlDataAdapter adapter = new SqlDataAdapter(sql, connection);  
        adapter.Fill(ds);  
        dataGridView1.DataSource = null;  
        dataGridView1.DataSource = ds.Tables[0];  
        connection.Close();  
    }  

    private void button4_Click(object sender, EventArgs e)  
    {  
        string value=comboBox1.SelectedItem.ToString();   
        int quantity=Convert.ToInt32(textBox1.Text);  
        connection.Open();  
        string sql = string.Format("select quantity_material from Materials where name_material='{0}'", value);  
        SqlCommand sqlCommand = new SqlCommand(sql, connection);  
        double getquantity =Convert.ToDouble(sqlCommand.ExecuteScalar());  
        double newquantity = getquantity - quantity;  
        sql = String.Format("update Materials set quantity_material={0} where name_material='{1}'", newquantity, value);  
        sqlCommand = new SqlCommand(sql,connection);  
        sqlCommand.ExecuteNonQuery();  
        Console.WriteLine(getquantity);  
        connection.Close();  

    }  
}  

Note: I don't have mysql database, I used sql database to replace it. You could make some changes based on my code.

Here is my tested result:

Best Regards,
Jack

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