String Interpolation in C#: A Cleaner Way to Format Strings

Understanding the difference between COUNT() and COUNT(DISTINCT) in SQL is crucial for accurate data analysis.

COUNT() returns the total number of rows that match your query criteria, including duplicates, while COUNT(DISTINCT) returns the number of unique values in a specified column, effectively eliminating duplicates from the count.

For example, if you have a table of customer orders where a single customer can place multiple orders, COUNT(customer_id) would give you the total number of orders, whereas COUNT(DISTINCT customer_id) would tell you how many unique customers have placed orders.

The choice between these functions depends on your specific reporting needs. Use COUNT() when you need the total number of records, such as counting all sales transactions or total number of website visits.

Use COUNT(DISTINCT) when you need to know unique occurrences, like the number of different products sold or unique visitors to your website. It's also worth noting that COUNT(*) counts all rows including NULL values, while COUNT(column_name) excludes NULL values from that specific column, which can lead to different results depending on your data structure.

Example

-- Example table: customer_orders
-- customer_id | order_date  | product_id
-- 1          | 2024-01-01  | 100
-- 1          | 2024-01-02  | 101
-- 2          | 2024-01-01  | 100
-- 3          | 2024-01-03  | 102

-- Count all orders
SELECT COUNT(*) as total_orders
FROM customer_orders;
-- Result: 4 (counts all rows)

-- Count unique customers who placed orders
SELECT COUNT(DISTINCT customer_id) as unique_customers
FROM customer_orders;
-- Result: 3 (counts unique customer_ids: 1, 2, 3)

-- Count unique products ordered
SELECT COUNT(DISTINCT product_id) as unique_products
FROM customer_orders;
-- Result: 3 (counts unique product_ids: 100, 101, 102)

-- Compare regular COUNT with COUNT DISTINCT
SELECT 
    COUNT(customer_id) as total_orders,
    COUNT(DISTINCT customer_id) as unique_customers
FROM customer_orders;
-- Result: total_orders = 4, unique_customers = 3

When working with URLs in C#, encoding is essential to ensure that special characters (like spaces, ?, &, and =) don’t break the URL structure. The recommended way to encode a string for a URL is by using Uri.EscapeDataString(), which converts unsafe characters into their percent-encoded equivalents.

string rawText = "hello world!";
string encodedText = Uri.EscapeDataString(rawText);

Console.WriteLine(encodedText); // Output: hello%20world%21

This method encodes spaces as %20, making it ideal for query parameters.

For ASP.NET applications, you can also use HttpUtility.UrlEncode() (from System.Web), which encodes spaces as +:

using System.Web;

string encodedText = HttpUtility.UrlEncode("hello world!");
Console.WriteLine(encodedText); // Output: hello+world%21

For .NET Core and later, Uri.EscapeDataString() is the preferred choice.

Reading a file line by line is useful when handling large files without loading everything into memory at once.

✅ Best Practice: Use File.ReadLines() which is more memory efficient.

Example

foreach (string line in File.ReadLines("file.txt"))
{
    Console.WriteLine(line);
}

Why use ReadLines()?

Reads one line at a time, reducing overall memory usage. Ideal for large files (e.g., logs, CSVs).

Alternative: Use StreamReader (More Control)

For scenarios where you need custom processing while reading the contents of the file:

using (StreamReader reader = new StreamReader("file.txt"))
{
    string? line;
    while ((line = reader.ReadLine()) != null)
    {
        Console.WriteLine(line);
    }
}

Why use StreamReader?

Lets you handle exceptions, encoding, and buffering. Supports custom processing (e.g., search for a keyword while reading).

When to Use ReadAllLines()? If you need all lines at once, use:

string[] lines = File.ReadAllLines("file.txt");

Caution: Loads the entire file into memory—avoid for large files!