使用GROUP BY計算組的百分比

Question

我正在對數據集執行GROUP BY和COUNT（*），並且我想計算每個組在總數上的百分比。

例如，在此查詢，我想知道有多少計數（）每個國家代表在總（從publicdata SELECT COUNT（）：samples.natality）：

SELECT state, count(*) 
FROM [publicdata:samples.natality] 
GROUP by state 

有幾種方法可以在SQL中完成，但我還沒有找到在BigQuery中實現它的方法，有誰知道嗎？

謝謝！

Answer 1

檢查RATIO_TO_REPORT，最近宣佈窗口功能之一：

SELECT state, ratio * 100 AS percent FROM (
SELECT state, count(*) AS total, RATIO_TO_REPORT(total) OVER() AS ratio 
FROM [publicdata:samples.natality] 
GROUP by state 
) 

state percent 
AL  1.4201828131159113 
AK  0.23521048665998198 
AZ  1.3332896746620975 
AR  0.7709591206172346 
CA  10.008298605982642 

Answer 2

您可以使用虛擬值作爲關鍵字，對總數進行自聯接。例如：

SELECT 
    t1.state AS state, 
    t1.cnt AS cnt, 
    100 * t1.cnt/t2.total as percent 
FROM (
    SELECT 
    state, 
    COUNT(*) AS cnt, 
    1 AS key 
    FROM 
    [publicdata:samples.natality] 
    WHERE state is not null 
    GROUP BY 
    state) AS t1 
JOIN (
    SELECT 
    COUNT(*) AS total, 
    1 AS key 
    FROM 
    [publicdata:samples.natality]) AS t2 
ON t1.key = t2.key 
ORDER BY percent DESC