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COLUMN pool    HEADING "Pool"
COLUMN name    HEADING "Name"
COLUMN sgasize HEADING "Allocated" FORMAT 999,999,999,999
COLUMN bytes   HEADING "Free" FORMAT 999,999,999,999
SET LINES 250

SELECT
    f.pool
  , f.name
  , s.sgasize
  , f.bytes
  , ROUND(f.bytes/s.sgasize*100, 2) "% Free"
FROM
    (SELECT SUM(bytes) sgasize, pool FROM v$sgastat GROUP BY pool) s
  , v$sgastat f
WHERE
    f.name = 'free memory'
  AND f.pool = s.pool;