Question

我的查询有LEFT JOIN，group by和ROLLUP，如下所示：

Select * from
(
    Select user_agent,
    value,
    recoqty,
    count(recoqty) as C
    from august_2016_search_stats SS
    LEFT JOIN august_2016_extra E
        on (SS.id = E.stats_id and E.key = 'personalized')
    where time >= '2016-08-22 00:00:00' and
          time <= '2016-08-22 23:59:59' and
          query_type = 'myfeed' and
          recoqty = 'topics'
    group by recoqty,
             user_agent,
             value
    with ROLLUP
    having recoqty is not null
) D
order by C desc;

给出如下结果：

+------------+-------+---------+------+
| user_agent | value | recoqty | C    |
+------------+-------+---------+------+
| NULL       | NULL  | topics  | 1330 |
| abscdef    | NULL  | topics  | 1330 |
| abscdef    | NULL  | topics  | 1285 |
| abscdef    | 1     | topics  |   25 |
| abscdef    | 0     | topics  |   20 |
+------------+-------+---------+------+

此处，值（NULL 1285）归因于LEFT JOIN，值（NULL 1330）归因于汇总。但是，是否有办法仅为NULL替换LEFT JOIN值，而不是ROLLUP？

Answer 1

这有点棘手，因为来自您的数据的NULL值似乎与来自汇总的NULL值无法区分。一种可能的解决方法是首先执行非聚合查询，使用NULL将value列中的'NA'值替换为COALESCE或其他占位符。然后使用汇总GROUP BY将其聚合为子查询。那么NULL列中的value值肯定会来自汇总，而不是您的实际数据。

SELECT t.user_agent,
       t.value,
       t.recoqty,
       t.C
FROM
(
    SELECT user_agent,
           COALESCE(value, 'NA') AS value
           recoqty,
           COUNT(recoqty) AS C
    FROM august_2016_search_stats SS
    LEFT JOIN august_2016_extra E
        ON SS.id = E.stats_id AND
              E.key = 'personalized'
    WHERE time >= '2016-08-22 00:00:00' AND
          time <= '2016-08-22 23:59:59' AND
          query_type = 'myfeed' AND
          recoqty = 'topics'
) t
GROUP BY t.recoqty,
         t.user_agent,
         t.value
WITH ROLLUP
HAVING t.recoqty IS NOT NULL

在LEFT JOIN中将默认值替换为NULL，但不在ROLLUP中

1 个答案: