How to Read a File Line by Line in C#?

When working with SQL Server, you may often need to count the number of unique values in a specific column. This is useful for analyzing data, detecting duplicates, and understanding dataset distributions.

Using COUNT(DISTINCT column_name)

To count the number of unique values in a column, SQL Server provides the COUNT(DISTINCT column_name) function. Here’s a simple example:

SELECT COUNT(DISTINCT column_name) AS distinct_count
FROM table_name;

This query will return the number of unique values in column_name.

Counting Distinct Values Across Multiple Columns

If you need to count distinct combinations of multiple columns, you can use a subquery:

SELECT COUNT(*) AS distinct_count
FROM (SELECT DISTINCT column1, column2 FROM table_name) AS subquery;

This approach ensures that only unique pairs of column1 and column2 are counted.

Why Use COUNT DISTINCT?

• Helps in identifying unique entries in a dataset.
• Useful for reporting and analytics.
• Efficient way to check for duplicates.

By leveraging COUNT(DISTINCT column_name), you can efficiently analyze your database and extract meaningful insights. Happy querying!

In C#, you can format an integer with commas (thousands separator) using ToString with a format specifier.

int number = 1234567;
string formattedNumber = number.ToString("N0"); // "1,234,567"
Console.WriteLine(formattedNumber);

Explanation:

"N0": The "N" format specifier stands for Number, and "0" means no decimal places. The output depends on the culture settings, so in regions where , is the decimal separator, you might get 1.234.567.

Alternative:

You can also specify culture explicitly if you need a specific format:

using System.Globalization;

int number = 1234567;
string formattedNumber = number.ToString("N0", CultureInfo.InvariantCulture);
Console.WriteLine(formattedNumber); // "1,234,567"

Using SqlDataReader asynchronously prevents blocking the main thread, improving performance in web apps and large queries. Here’s how to do it properly.

Use await with ExecuteReaderAsync()

using (SqlConnection conn = new SqlConnection(connectionString))
{
    await conn.OpenAsync();
    using (SqlCommand cmd = new SqlCommand("SELECT * FROM Users", conn))
    using (SqlDataReader reader = await cmd.ExecuteReaderAsync()) 
    {
        while (await reader.ReadAsync()) 
        {
            Console.WriteLine(reader["Username"]);
        }
    } // ✅ Auto-closes reader
} // ✅ Auto-closes connection

Why use async?

A couple of reasons:

• Frees up the thread while waiting for the database.
• Improves scalability in ASP.NET Core and web apps.

⚡ Alternative: ConfigureAwait(false) for ASP.NET

Use ConfigureAwait(false) in library code to avoid deadlocks in UI frameworks like ASP.NET.

using (SqlConnection conn = new SqlConnection(connectionString))
{
    await conn.OpenAsync().ConfigureAwait(false);
    using (SqlCommand cmd = new SqlCommand("SELECT * FROM Users", conn))
    using (SqlDataReader reader = await cmd.ExecuteReaderAsync().ConfigureAwait(false)) 
    {
        while (await reader.ReadAsync().ConfigureAwait(false)) 
        {
            Console.WriteLine(reader["Username"]);
        }
    }
}