In the grouping and lesson within this course, we wanted to pull out the row that had the earliest `create_date`. If we do `select min(create_date)`, and then pull ...

ERROR: subquery in FROM must have an alias at character 22 HINT: For example, FROM (SELECT ...) [AS] foo. STATEMENT: SELECT COUNT(*) FROM (SELECT b.bssid, AVG(b.signal_strength_average) AS ...

The argument of EXISTS is an arbitrary SELECT statement, or subquery. The subquery is evaluated to determine whether it returns any rows. If it returns at least one row, the result of EXISTS is "true" ...