SQL “Join” on null values

Question

For reasons beyond my control, I need to join two tables and I need null values to match. The best option I could think of was to spit out a UUID and use that as my comparis

Answer 1

Do you really want to be able to join the tables if a value is null? Can't you just exclude the possible null values in the join predicate? I find it hard to grok that rows in two tables can be related by a null value. If you have 100 nulls in table1.col_a and 100 nulls in table2.col_b, you're going to have 10000 rows returned just for the rows with null. It sounds incorrect.

However, you did say you need it. Can I suggest coalescing the null column into a smaller string as character comparisons are relatively expensive. Even better, coalesce the nulls into an integer if the data in the columns is going to be text. Then you have very quick 'comparisons' and you're unlikely to collide with existing data.