Question

我有以下查询：

'select team, count(distinct id) as distinct_id_count_w1 from myTable where timestamp > t1  and timestamp < t2 group by team'

'select team, count(distinct id) as distinct_id_count_w2 from myTable where timestamp > t2  and timestamp < t3 group by team'

是否可以将这两个查询合并为一个？谢谢！

Answer 1

很容易:)这应该适用于大多数常见的数据库引擎：

select team, count(distinct id) as distinct_id_count_w1, null as distinct_id_count_w2 from myTable where timestamp > t1  and timestamp < t2 group by team

UNION ALL

select team, null as distinct_id_count_w1, count(distinct id) as distinct_id_count_w2 from myTable where timestamp > t2  and timestamp < t3 group by team

正如Edamame所说，你可能想要阅读每个团队的两个结果。问题本身并不清楚，但可以通过这种方式解决：

SELECT
    COALESCE(interval1.team interval2.team) AS team,
    interval1.distinct_id_count_w1,
    interval2.distinct_id_count_w2
FROM (
    select team, count(distinct id) as distinct_id_count_w1 from myTable where timestamp > t1  and timestamp < t2 group by team
) AS interval1
FULL OUTER JOIN
(
    select team, count(distinct id) as distinct_id_count_w2 from myTable where timestamp > t2  and timestamp < t3 group by team
) AS interval2
ON interval1.team IS NULL OR interval2.team IS NULL OR interval1.team = interval2.team

Answer 2

如果你认为返回的结果不同，你应该使用“UNION ALL”，因为你只使用“UNION”，sql会区分结果以影响查询的性能

SQL / Impala：将多个查询（具有不同的where子句）组合成一个

2 个答案: