Selecting all files in Finder with column view
It depends on the way the folder (or other folder-like item) is selected. If you select an item by clicking on it, command-A selects all items in the next column. If you select an item with the keyboard (or by for example revealing a folder in Finder from another application), command-A selects all items in the same column.

You can select all items in the current column by pressing the up or down arrow key and then command-A, or all items in the next column by pressing the right arrow key and then command-A.