Gold Medals by Demographic Group
(Western European Countries Only)
+----------+--------------------+-------+
| season | demographic_group | golds |
|----------+--------------------+-------|
| Winter | Male Age 26+ | 13 |
| Winter | Female Age 26+ | 8 |
| Summer | Male Age 13-25 | 7 |
| Summer | Female Age 13-25 | 6 |
| Winter | Male Age 13-25 | 4 |
| Summer | Male Age 26+ | 4 |
| Winter | Female Age 13-25 | 4 |
| Summer | Female Age 26+ | 2 |
+----------+--------------------+-------+
相關資料表
相關資料表
作法 A：先 JOIN，後 UNION
作法 A：先 JOIN，後 UNION
步驟 1： 以 JOIN 建立上半段查詢
SELECT
athlete_id,
gender,
age,
gold
FROM summer_games AS sg
JOIN athletes AS a
ON sg.athlete_id = a.id;
Query ran successfully!
作法 A：先 JOIN，後 UNION
步驟 2： 建立下半段查詢，並以 UNION 合併兩者
SELECT
athlete_id,
gender,
age,
gold
FROM summer_games AS sg
JOIN athletes AS a
ON sg.athlete_id = a.id
UNION ALL
SELECT
athlete_id,
gender,
age,
gold
FROM winter_games AS wg
JOIN athletes AS a
ON wg.athlete_id = a.id;
作法 B：先 UNION，後 JOIN
作法 B：先 UNION，後 JOIN
步驟 1： 建立最初的 UNION
SELECT
athlete_id,
gold
FROM summer_games AS sg
UNION
SELECT
athlete_id,
gold
FROM winter_games AS wg;
作法 B：先 UNION，後 JOIN
步驟 2： 轉為子查詢並 JOIN
SELECT
athlete_id,
gender,
age,
gold
FROM
(SELECT
athlete_id,
gold
FROM summer_games AS sg
UNION ALL
SELECT athlete_id, gold
FROM winter_games AS wg) AS g
JOIN athletes AS a
ON g.athlete_id = a.id;
比較
作法 A
SELECT
athlete_id,
gender,
age,
gold
FROM summer_games AS sg
JOIN athletes AS a
ON sg.athlete_id = a.id
UNION ALL
SELECT
athlete_id,
gender,
age,
gold
FROM winter_games AS wg
JOIN athletes AS a
ON wg.athlete_id = a.id;
作法 B
SELECT
athlete_id,
gender,
age,
gold
FROM
(SELECT
athlete_id,
gold
FROM summer_games AS sg
UNION ALL
SELECT athlete_id, gold
FROM winter_games AS wg) AS g
JOIN athletes AS a
ON g.athlete_id = a.id;
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