,CASE
WHEN m.COMPLETED_DT is NULL THEN ''
WHEN m.COMPLETED_DT <= m.SLA_ADJUSTED_DT  THEN 'SLA Met'
WHEN m.SLA_ADJUSTED_DT IS NULL THEN 'SLA Met'
ELSE 'SLA Missed' END AS "SLA Desc"

SELECT (count(*) * 100 / (select count(*) from testtable)) as YesSLA FROM testtable where SLA='Yes';