What is the second argument in array_length() function?
That's array's dimension.
Consider an example with a 2D array 3×2:
array_length(array[[1, 2], [3, 4], [5, 6]], 1) ---> 3array_length(array[[1, 2], [3, 4], [5, 6]], 2) ---> 2The size of the first dimension is 3; the size of the second dimension is 2.