If I am not wrong, this is the best practice because of the following reasons:

1. It fetches only the required columns, reducing the amount of data transferred. By doing this, it also limits the possible exposure of sensitive data.
2. SQL keywords should be consistently capitalized to improve readability.

Maybe for this particular case, using '*' after the keyword 'SELECT' could lead to the same result, but I think it is good to develop the habit of just fetching the required columns by using their names and thus avoiding the possible fetching of unnecessary or sensible data.

Not the Best Practices definatly

This solution only fits on a single line but forces the array to be traversed twice.

This seems quciker then what i wrote lol

In theory, yes. Bust in many cases the time saved by using a wildcard is more important. Plus, you can limit your sample to, let's say, 100 rows and not worry about how many columns you have there anymore.

Use what your language offers you. Codewars uses PostgreSQL and I will use LIMIT if PostgreSQL allows me. It is infinitely more readable than your solution.

right? i test it too. it not work with last test

Doesn't work for:
$this->assertEquals([], solution(""));

This does not check if the array is a valid matrix

Not best practice because this mutates the original array.