使用where子句条件计算中位数 - sqlite

Question

我正在尝试根据 sqlite -[=12= 中的 table 计算平均停留时间和平均总花费 (Room_Spend + Food_Spend) ]

CREATE TABLE test (
    Stay Int,
    Residence Text,
    Purpose TEXT,
    Room_Spend INT,
    Food_Spend INT);
    
INSERT INTO test (Stay, Residence, Purpose, Room_Spend, Food_Spend) VALUES (10, 'Italy', 'Business', 5, 5);   
INSERT INTO test (Stay, Residence, Purpose, Room_Spend, Food_Spend) VALUES (2, 'Italy', 'Leisure', 0, 0);  
INSERT INTO test (Stay, Residence, Purpose, Room_Spend, Food_Spend) VALUES (5, 'Italy', 'Leisure', 0, 0);  
INSERT INTO test (Stay, Residence, Purpose, Room_Spend, Food_Spend) VALUES (10, 'Germany', 'Business', 0, 0);  
INSERT INTO test (Stay, Residence, Purpose, Room_Spend, Food_Spend) VALUES (3, 'Germany', 'Business', 1, 1);
INSERT INTO test (Stay, Residence, Purpose, Room_Spend, Food_Spend) VALUES (5, 'Germany', 'Business', 1, 1);

我是 sql 的新手，这就是我所拥有的：

SELECT AVG(Stay)
FROM (SELECT stay, Residence
      FROM test
      ORDER BY stay
      LIMIT 2 - (SELECT COUNT(*) FROM test) % 2    -- odd 1, even 2
      OFFSET (SELECT (COUNT(*) - 1) / 2))

非常感谢任何帮助！

Answer 1

一种方法使用解析函数：

WITH cte AS (
    SELECT *, ROW_NUMBER() OVER (ORDER BY Stay) rn,
              COUNT(*) OVER () AS cnt,
              AVG(Room_Spend + Food_Spend) OVER () AS total_spent
    FROM test
)

SELECT AVG(Stay) AS Stay, MAX(total_spent) AS total_spent
FROM cte
WHERE rn = (cnt / 2) + 1 AND cnt % 2 = 1 OR
      rn IN (cnt / 2, cnt / 2 + 1) AND cnt % 2 = 0;

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