Effects of NULL for Multiple Assignments - SQL
If the row expression given as the source for a multiple assignment evaluates to NULL, then NULL is assigned to each target. If a SELECT ... INTO statement results in an empty table, then the target variables are not updated and a completion condition is given to indicate that. This is not exactly an "effect of NULL", of course, but I mention it here because of the contrast with a row subquery, which delivers a single row with NULL for each field when its table expression evaluates to an empty table. This observation might influence the choice between SET and SELECT ... INTO.