I need to update multiple columns (~250) from one table to another based on a two-column key. In Postgres I would write this using the FROM clause, but since MonetDB doesn't support the FROM clause, I've successfully updated one column with:

My question is whether there is any benefit to writing a multiple column update into a single UPDATE statement:

UPDATE target_table

SET column1 = (SELECT column1 FROM source_table WHERE target_table.key = source_table.key),

column2 = (SELECT column2 FROM source_table WHERE target_table.key = source_table.key),

On Postgres I believe the multi-column update using a table join would only have to do the sequential scan of each table once, but with the necessity of sub-selects in MonetDB, what is the backend doing? Is it already doing an index scan once for each row in the single column case, then doing it once for each row * column in the multi-column case?

Best,

--Lee