标签:goal country away 查询 goals home query SELECT Sub
WHERE 子查询
SELECT
-- Select the date, home goals, and away goals scored
date,
home_goal,
away_goal
FROM matches_2013_2014
-- Filter for matches where total goals exceeds 3x the average
WHERE (home_goal + away_goal) >
(SELECT 3 * AVG(home_goal + away_goal)
FROM matches_2013_2014);
FROM子查询
SELECT
-- Select country name and the count match IDs
c.name AS country_name,
COUNT(sub.id) AS matches
FROM country AS c
-- Inner join the subquery onto country
-- Select the country id and match id columns
INNER JOIN (SELECT country_id, id
FROM match
-- Filter the subquery by matches with 10+ goals
WHERE (home_goal + away_goal) >= 10) AS sub
ON c.id = sub.country_id
GROUP BY country_name;
- 可以看做:SELECT FROM country 的结果INNER JOIN 子查询表
- county表和sub表用c.id连接,c.id只需要在country表中存在即可,不需要出现在最终的select结果中
SELECT
-- Select country, date, home, and away goals from the subquery
country,
date,
home_goal,
away_goal
FROM
-- Select country name, date, and total goals in the subquery
(SELECT name AS country,
m.date,
m.home_goal,
m.away_goal,
(m.home_goal + m.away_goal) AS total_goals
FROM match AS m
LEFT JOIN country AS c
ON m.country_id = c.id) AS subq
-- Filter by total goals scored in the main query
WHERE total_goals >= 10;
- FROM后的子查询为一个整体,区别上面的例子;
- 最终的筛选条件是WHERE total_goals >= 10,虽然total_goals没有出现在SELECT的结果中,但是from ()AS subq的一个字段,也ok
SELECT 子查询
SELECT
l.name AS league,
-- Select and round the league's total goals
ROUND(AVG(m.home_goal + m.away_goal), 2) AS avg_goals,
-- Select & round the average total goals for the season
(SELECT ROUND(AVG(home_goal + away_goal), 2)
FROM match
WHERE season = '2013/2014') AS overall_avg
FROM league AS l
LEFT JOIN match AS m
ON l.country_id = m.country_id
-- Filter for the 2013/2014 season
WHERE season = '2013/2014'
- 主查询中的ROUND(AVG(m.home_goal + m.away_goal), 2) AS avg_goals是每个league的avg goal;
- 子查询的目的是:计算整个dataset的平均值,不考虑子查询外的限制条件
子查询Everywhere
SELECT
-- Select the stage and average goals from s
s.stage,
ROUND(s.avg_goals,2) AS avg_goal,
-- Select the overall average for 2012/2013
(SELECT AVG(home_goal + away_goal) FROM match WHERE season = '2012/2013') AS overall_avg
FROM
-- Select the stage and average goals in 2012/2013 from match
(SELECT
stage,
AVG(home_goal + away_goal) AS avg_goals
FROM match
WHERE season = '2012/2013'
GROUP BY stage) AS s
WHERE
-- Filter the main query using the subquery
s.avg_goals > (SELECT AVG(home_goal + away_goal)
FROM match WHERE season = '2012/2013');
WHERE和SELECT语句中出现子查询:
(SELECT AVG(home_goal + away_goal)
FROM match WHERE season = ‘2012/2013’)
都是为了计算overall AVG =》 不受到stage的影响下
使用多个subquery要注意
每个子查询都要filter上 where necessary
标签:goal,country,away,查询,goals,home,query,SELECT,Sub 来源: https://blog.csdn.net/Cecilia_W422/article/details/88602629
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