Good to know... I didn't know about the importance of the order of the column names inside the brakets.
But if I had a table with four columns:
column_1 - column_2 - on_what_id - on_which_table
Additionally I had an index of the kind I mentioned above and four rows were inserted in that table.
The first two rows had values in column_1 and column_2 BUT NULL for on_which_table and on_what_id.
The last two had values in all four columns.
I heard that in case of NULLs in indexed columns the index will not be used!? What if there was a '' instead of a NULL in the first two columns?
