Postgres function assign query results to multiple variables
As said in  "40.5.3. Executing a Query with a Single-row Result" (emphasis mine):


  The result of a SQL command yielding a single row (possibly of multiple columns) can be assigned to a record variable, row-type variable, or list of scalar variables. This is done by writing the base SQL command and adding an INTO clause.


So this should work:

SELECT col1, col2 INTO a, b FROM tbl WHERE...;