How to find top SQL by disk reads per execution in Oracle

V$SQLAREA is licence-free — every edition has it. This ranks SQL by disk reads per execution, which highlights heavy statements even when only one execution has run. Prompts for how many rows to return.

SELECT *
FROM (
  SELECT SUBSTR(a.sql_text, 1, 50) AS sql_text,
         TRUNC(a.disk_reads / DECODE(a.executions, 0, 1, a.executions)) AS reads_per_execution,
         a.buffer_gets,
         a.disk_reads,
         a.executions,
         a.sorts,
         a.address
  FROM   v$sqlarea a
  ORDER BY 2 DESC
)
WHERE rownum <= &&top_n;