mysql根据某个字段去重

在有主键的情况下

SELECT * FROM sa_request t WHERE t.logid IN (
 SELECT MAX(logid) FROM sa_request GROUP BY caseid
);

或者效率高些的

SELECT * FROM sa_request t WHERE EXISTS (
  SELECT 1 FROM sa_request  GROUP BY caseid
  HAVING MAX(logid) = t.logid
);