SQL / Impala：將多個查詢（具有不同的where子句）組合為一個

Question

我有以下查詢：

'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'

是否可以將這兩個查詢合並為一個？ 謝謝！

Answer 1

輕松:)這應該適用於大多數常見的數據庫引擎：

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所說，您可能希望每個團隊閱讀兩個結果。 從問題本身尚不清楚，但是可以通過以下方式解決：

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

如果您認為返回的結果不同，則應使用“ UNION ALL”，因為您只能與“ UNION”一起使用，sql將區分結果以影響查詢的性能