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.
To count the number of unique values in a column, SQL Server provides the COUNT(DISTINCT column_name) function. Here’s a simple example:
COUNT(DISTINCT column_name)
SELECT COUNT(DISTINCT column_name) AS distinct_count FROM table_name;
This query will return the number of unique values in column_name.
column_name
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.
column1
column2
By leveraging COUNT(DISTINCT column_name), you can efficiently analyze your database and extract meaningful insights. Happy querying!
Raw string literals in C# provide a flexible way to work with multiline strings, with some interesting rules around how quotes work.
The key insight is that you can use any number of double quotes (three or more) to delimit your string, as long as the opening and closing sequences have the same number of quotes.
"""
// Three quotes - most common usage string basic = """ This is a basic multiline string """; // Four quotes - when your content has three quotes string withThreeQuotes = """" Here's some text with """quoted""" content """"; // Five quotes - when your content has four quotes string withFourQuotes = """"" Here's text with """"nested"""" quotes """""; // Six quotes - for even more complex scenarios string withFiveQuotes = """""" Look at these """""nested""""" quotes! """""";
The general rule is that if your string content contains N consecutive double quotes, you need to wrap the entire string with at least N+1 quotes. This ensures the compiler can properly distinguish between your content and the string's delimiters.
// Example demonstrating the N+1 rule string example1 = """ No quotes inside """; // 3 quotes is fine string example2 = """" Contains """three quotes""" """"; // Needs 4 quotes (3+1) string example3 = """"" Has """"four quotes"""" """""; // Needs 5 quotes (4+1)
// Indentation example string properlyIndented = """ { "property": "value", "nested": { "deeper": "content" } } """; // This line's position determines the indentation
This flexibility with quote counts makes raw string literals extremely versatile, especially when dealing with content that itself contains quotes, like JSON, XML, or other structured text formats.
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.
Storing passwords as plain text is dangerous. Instead, you should hash them using a strong, slow hashing algorithm like BCrypt, which includes built-in salting and resistance to brute-force attacks.
Step 1: Install BCrypt NuGet Package
Before using BCrypt, install the BCrypt.Net-Next package:
dotnet add package BCrypt.Net-Next
or via NuGet Package Manager:
Install-Package BCrypt.Net-Next
Step 2: Hash a Password
Use BCrypt.HashPassword() to securely hash a password before storing it:
using BCrypt.Net; string password = "mySecurePassword123"; string hashedPassword = BCrypt.HashPassword(password); Console.WriteLine(hashedPassword); // Output: $2a$12$...
Step 3: Verify a Password
To check a user's login attempt, use BCrypt.Verify():
bool isMatch = BCrypt.Verify("mySecurePassword123", hashedPassword); Console.WriteLine(isMatch); // Output: True
Ensuring proper hashing should be at the top of your list when it comes to building authentication systems.
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