C# 与 MySQL。 从 MySQL 表中获取有关单元格、行及其值的信息

Question

I'm making application with C# Windows forms with MySQL and I need advices how should I implement the next:

1. I need to find the biggest and the largest decimal values from the whole column which could contain any amount of values. I need to get them to some sort of array or list (?) and then study them or it is better to make it with MySQL commands?

2. I need to calculate the sum (or do any other math operation) of all decimal values from MySQL column values.

And in general where is the best way to do this operations? on the MySQL side or on the WinForms side?

Answer 1

Depending on your business logic and program design, it can be done on either end. in case of MySql a stored procedure can be created that performs the functionality that you require, and that SP can later be called in your code to produce the results. if you wish to do that in your winforms app, I'd prefer to use Entity framework to access the data and then use LINQ to perform the functionality that you require.

Answer 2

You can use the System.Data.MySqlClient namespace to interact with MySQL databases.

Making the calculations on the database side or not is up to you, just know that if you have a large number of records in the table this will take some time.

What I usually do is a simple SELECT and than iterate through the rows on what returns to process the data. You can use the MySqlDataAdapter to get a DataTable to do so.

DataTable dt = new DataTable();

using(var dataAdapter = new MySqlDataAdapter("SELECT decimals FROM myTable", myConnectionString)) {
    dataAdapter.Fill(dt); //fills the datatable
    double allDoubles = 0.0; // stores the sum

DataTable dt = new DataTable();

using(var dataAdapter = new MySqlDataAdapter("SELECT SUM(decimals) FROM myTable", connectionString)) { dataAdapter.Fill(dt); //fills the datatable double myDoubleSum = 0.0; // stores the sum

allDoubles = Convert.ToDouble(row[0].ToString()); 

} }

As people said in the comments, you can also do it by using the SUM function which if indexed, will take none to no time at all to complete.

DataTable dt = new DataTable();

using(var dataAdapter = new MySqlDataAdapter("SELECT SUM(decimals) FROM myTable", connectionString)) {
    dataAdapter.Fill(dt); //fills the datatable
    double myDoubleSum = 0.0; // stores the sum

    allDoubles = Convert.ToDouble(row[0].ToString()); 
}