比较两三个字段的最大值

SELECT d.id,
       (SELECT    MAX(maxtimes)
          FROM      ( VALUES ( d.t1), ( d.t2),
                    ( d.t3) ) AS times ( maxtimes )
       ) AS times
FROM(
SELECT a.times AS t1, b.times AS t2,c.times AS t3,a.id FROM a
LEFT JOIN  b ON b.id = a.id
LEFT JOIN  b ON a.id = c.id
) d