I have one table named 'posts' and one table named 'threads'. Both have the column called 'total_id' which is an integer.
Now, how to get from those two tables the 1 highest value (max) in the 'total_id' column? (MySQL)
You can get it as follows:
SELECT Greatest( (SELECT Max(total_id) FROM posts), (SELECT Max(total_id) FROM threads) )