SQL /帕拉：合併多個查詢（用不同的WHERE子句中）到一個

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' 

是否有可能這兩個查詢合併成一個？謝謝！

Answer 1

輕鬆:)這應該上最常見的數據庫引擎的工作原理：

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 

如毛豆說，你可能需要閱讀每隊兩個結果。這是不是從問題本身清楚，但可以用此方式解決：

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u認爲，返回的結果是不同的，U應使用「UNION ALL」，因爲ü只能用「聯盟」的工作，SQL將區分結果以影響查詢