It's because this kata is using postgresql, and has sqlite disabled. I'd rather this kata be categorized as PostgreSQL then, to be honest, this threw me off too.

He's right, read the other note:

Don't forget to convert the percent parameter as a percentage in the body of your function: if the parameter percent is 2 you have to convert it to 0.02.

Very naive of you not to read instructions.

"There are no fractions of people. At the end of each year, the population count is an integer: 252.8 people round down to 252 persons."

thanks for taking the time to reply!

Essentially, there is no difference between string and String (capital S) in C#.

String (capital S) is a class in the .NET framework in the System namespace. The fully qualified name is System.String. Whereas, the lower case string is an alias of System.String.

Many developers use string to declare variables in C# and use System.String class to use any built-in string methods e.g., String.IsNullOrEmpty().

Should string be lowercase in the string.Join section? I understand it's being used as a method but it's from System. By convention, primitive data types like int, double, bool, and string are written in lowercase. This consistent casing helps distinguish them from user-defined classes. Is there an exception here?

I didn't think it was that simple

Yes, but I don't like the one line functions, it's easier to read by the standard design.

When you think your code (2lines) is short. You submit and find out that someone else code is much shorter

https://www.postgresql.org/docs/15/functions-string.html, you can also use the site's search functionality.

really?
what if there will be a List with values {1, -1, 2, -2, 3, -3, 3}?

That may be the gist of the problem, but the problem states 'The string has a length greater or equal to one and contains only letters from a to z.' Adding extra error handling for other symbols and capital letters is not optimal as it's assumed this is already handled before the string is passed in.

Providing invalid characters to the input string is what the problem is all about

Guys where should i go to find all these function names such as to_hax() and translate() ?
Is there a comprehensive list of them?

Nicely done