SQL explain plan: what is Materialize?

Question

I asked PostgreSQL to explain my query. Part of the explanation was:

table_name --> Materialize

What does materialize do? I\'m joining t

Answer 1

It means that it can't use any index (or similar method) to make the join efficient, so as a last resort is materializes the result from one of the tables to have a smaller set to work with when joining against the other table.