Code to look for gaps in records in a table

WITH aquery AS
(SELECT emailid after_gap,
LAG(emailid,1,0) OVER (ORDER BY emailid) before_gap
FROM lgncc_emaildetails)
SELECT
before_gap, after_gap
FROM
aquery
WHERE
before_gap != 0
AND
after_gap – before_gap > 1
ORDER BY
before_gap;

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