Question

db2语句 这两个语句的结果可以合并成一句sql么

SELECT colname, COUNT(1) AS a FROM tablename1 GROUP BY colname ORDER BY a DESC fetch first 3 rows only
SELECT colname, COUNT(1) AS a FROM tablename2 GROUP BY colname ORDER BY a DESC fetch first 3 rows only

Answer 1

SELECT colname, COUNT(1) AS a
FROM (
select colname from tablename1 union all
select colname from from tablename2
) t
GROUP BY colname
ORDER BY a DESC
fetch first 3 rows only