SQL笔记续补

时间 2020-11-23

标签 api 函数 spa code rem class date 栏目 SQL 繁體版

原文原文链接

case when then

等价于if xxx return xxx else xxxapi

就是按条件进行筛选函数

-- Identify the home team as Bayern Munich, Schalke 04, or neither
SELECT 
    CASE WHEN hometeam_id = 10189 THEN 'FC Schalke 04'  #简单的来讲就是按照条件进行查询
         WHEN hometeam_id = 9823 THEN 'FC Bayern Munich'
         ELSE 'Other' END AS home_team,
	COUNT(id) AS total_matches
FROM matches_germany
-- Group by the CASE statement alias
GROUP BY home_team;

demospa

SELECT 
	c.name AS country,
    -- Count games from the 2012/2013 season
	COUNT(CASE WHEN m.season = '2012/2013' 
          	   THEN m.id ELSE NULL END) AS matches_2012_2013
FROM country AS c
LEFT JOIN match AS m
ON c.id = m.country_id
-- Group by country name alias
GROUP BY country;

country	matches_2012_2013
Portugal	240
France	380
Scotland	228
Netherlands	306
Spain	380
Belgium	240
Italy	380
Germany	306
England	380
Switzerland	180
Poland	240
Showing 11 out of 11 rows

SELECT 
	m.date,
	--Select the team long name column and call it 'opponent'
	t.team_long_name AS opponent, 
	-- Complete the CASE statement with an alias
	CASE WHEN m.home_goal > m.away_goal THEN 'Home win!'
         WHEN m.home_goal < m.away_goal THEN 'Home loss :('
         ELSE 'Tie' END AS outcome
FROM matches_spain AS m
-- Left join teams_spain onto matches_spain
LEFT JOIN teams_spain AS t  #两个列表根据id进行合并
ON m.awayteam_id = t.team_api_id;


date	          outcome
2012-01-21	Home loss :(
2012-01-22	Home win!
2012-01-22	Home loss :(
2012-01-23	Home win!
2012-01-21	Tie
2012-01-22	Tie
2012-01-21	Home loss :(
2012-01-21	Home win!
2012-01-22	Tie
2012-01-22	Home loss :(
2011-10-26	Tie
2011-10-27	Home win!
2011-10-26	Home loss :(
2011-10-26	Home win!
2011-10-27	Home win!
2011-10-26	Home win!
2011-10-25	Tie
2011-10-26	Home loss :(
2011-10-26	Home win!
2011-10-25	Home loss :(
2011-10-30	Home win!
2011-10-30	Home win!
2011-10-30	Tie
2011-10-29	Home loss :(
2011-10-30	Home win!
2011-10-29	Home win!
2011-10-31	Home loss :(
2011-10-29	Home win!
2011-10-30	Home win!
2011-10-29	Home win!
2011-11-06	Home win!
2011-11-06	Tie
2011-11-06	Home win!
2011-11-06	Tie
2011-11-05	Tie
2011-11-05	Home loss :(
2011-11-05	Tie
2011-11-06	Tie
2011-11-06	Home win!
2011-11-06	Tie
2011-11-20	Tie
2011-12-07	Tie
2011-11-20	Home win!
2011-11-19	Home win!
2011-11-20	Home loss :(
2011-11-19	Home loss :(
2011-11-21	Home loss :(
2011-11-19	Home win!
2011-11-20	Tie
2011-11-20	Home win!
2011-11-27	Home loss :(
2011-11-27	Home win!
2011-11-27	Home win!
2011-11-27	Home loss :(
2011-11-27	Home loss :(
2011-11-26	Home win!
2011-11-28	Home win!
2011-11-27	Home loss :(
2011-11-26	Home loss :(
2011-11-26	Home win!
2011-12-04	Home win!
2011-12-03	Home win!
2011-12-05	Home win!
2011-12-03	Home win!
2011-12-03	Home win!
2011-12-04	Home win!
2011-12-04	Tie
2011-12-03	Home loss :(
2011-12-04	Home win!
2011-12-04	Home win!
2011-12-11	Tie
2011-12-11	Home loss :(
2011-12-11	Home loss :(
2011-12-11	Tie
2011-12-11	Home win!
2011-12-11	Home win!
2011-12-10	Home win!
2011-12-10	Home win!
2011-12-11	Tie
2011-12-10	Home loss :(
2011-12-17	Home loss :(
2011-12-18	Tie
2011-12-18	Home win!
2011-12-18	Home loss :(
2011-12-17	Home loss :(
2011-12-18	Home win!
2011-12-17	Home win!
2011-11-29	Home win!
2011-12-18	Home win!
2011-12-17	Home loss :(
2012-01-08	Tie
2012-01-07	Tie
2012-01-07	Home win!
2012-01-08	Home win!
2012-01-08	Tie
2012-01-08	Home win!
2012-01-07	Tie
2012-01-08	Tie
2012-01-07	Tie
2012-01-07	Home win!
Showing 100 out of 380 rows

demo2code

SELECT 
	date,
	-- Identify the home team as Barcelona or Real Madrid
	CASE WHEN hometeam_id = 8634 THEN 'FC Barcelona' 
         ELSE 'Real Madrid CF' END AS home,
    -- Identify the away team as Barcelona or Real Madrid
	CASE WHEN awayteam_id = 8634 THEN 'FC Barcelona' 
         ELSE 'Real Madrid CF' END AS away
FROM matches_spain
WHERE (awayteam_id = 8634 OR hometeam_id = 8634)
      AND (awayteam_id = 8633 OR hometeam_id = 8633); -- where 后面通常填写各类条件，简单的条件

date	home	away
2011-12-10	Real Madrid CF	FC Barcelona
2012-04-21	FC Barcelona	Real Madrid CF

demo3ip

SELECT
	date,
	CASE WHEN hometeam_id = 8634 THEN 'FC Barcelona' 
         ELSE 'Real Madrid CF' END as home,
	CASE WHEN awayteam_id = 8634 THEN 'FC Barcelona' 
         ELSE 'Real Madrid CF' END as away,
	-- Identify all possible match outcomes
	CASE WHEN home_goal > away_goal AND hometeam_id = 8634 THEN 'Barcelona win!'
         WHEN home_goal > away_goal AND hometeam_id = 8633 THEN 'Real Madrid win!' -- 不少的筛选的条件
         WHEN home_goal < away_goal AND awayteam_id = 8634 THEN 'Barcelona win!'
         WHEN home_goal < away_goal AND awayteam_id = 8633 THEN 'Real Madrid win!'
         ELSE 'Tie!' END AS outcome
FROM matches_spain
WHERE (awayteam_id = 8634 OR hometeam_id = 8634)
      AND (awayteam_id = 8633 OR hometeam_id = 8633);

date	home	away	outcome
2011-12-10	Real Madrid CF	FC Barcelona	Barcelona win!
2012-04-21	FC Barcelona	Real Madrid CF	Real Madrid win!

Filtering your CASE statement

过滤数据ci

-- Select team_long_name and team_api_id from team
SELECT
	team_long_name,
	team_api_id
FROM teams_italy
-- Filter by team long name
WHERE team_long_name = 'Bologna';

team_long_name	team_api_id
Bologna	9857

demo1rem

-- Select the season and date columns
SELECT 
	season,
	date,
    -- Identify when Bologna won a match
	CASE WHEN hometeam_id = 9857 AND home_goal > away_goal THEN 'Bologna Win'
         WHEN awayteam_id = 9857 AND away_goal > home_goal THEN 'Bologna Win' 
         END AS outcome
FROM matches_italy;

demo2it

-- Select the season, date, home_goal, and away_goal columns
SELECT 
	season,
	date,
	home_goal,
	away_goal
FROM matches_italy
WHERE
-- Exclude games not won by Bologna
	CASE WHEN hometeam_id = 9857 AND home_goal > away_goal THEN 'Bologna Win'
         WHEN awayteam_id = 9857 AND away_goal > home_goal THEN 'Bologna Win' 
         END IS NOT NULL;

season	date	home_goal	away_goal
2011/2012	2011-10-30	3	1
2011/2012	2011-12-04	1	0
2011/2012	2012-01-08	2	0
2011/2012	2012-02-21	2	0
2011/2012	2012-02-17	0	3
2011/2012	2012-04-12	1	0
2011/2012	2012-04-29	3	2
2011/2012	2012-05-02	0	1
2011/2012	2012-05-06	2	0
2011/2012	2011-10-16	0	2
2011/2012	2011-10-26	0	1
2012/2013	2012-11-18	3	0
2012/2013	2012-12-02	2	1
2012/2013	2012-12-16	2	3
2012/2013	2013-01-12	4	0
2012/2013	2013-02-03	2	3
2012/2013	2013-02-26	2	1
2012/2013	2013-03-03	3	0
2012/2013	2013-03-10	0	1
2012/2013	2012-09-16	2	3
2012/2013	2013-05-12	0	2
2012/2013	2012-09-30	4	0
2013/2014	2013-10-30	0	3
2013/2014	2013-12-22	1	0
2013/2014	2014-02-09	1	2
2013/2014	2014-03-23	1	0
2013/2014	2013-10-27	1	0

case when + 聚合函数

SELECT 
	c.name AS country,
    -- Count matches in each of the 3 seasons
	COUNT(CASE WHEN m.season = '2012/2013' THEN m.id END) AS matches_2012_2013,
	COUNT(CASE WHEN m.season = '2013/2014' THEN m.id END) AS matches_2013_2014,
	COUNT(CASE WHEN m.season = '2014/2015' THEN m.id END) AS matches_2014_2015
FROM country AS c
LEFT JOIN match AS m
ON c.id = m.country_id
-- Group by country name alias
GROUP BY country;

country	matches_2012_2013
Portugal	240
France	380
Scotland	228
Netherlands	306
Spain	380
Belgium	240
Italy	380
Germany	306
England	380
Switzerland	180
Poland	240
Showing 11 out of 11 rows

AS 后面每每都是新增的列，或者说按照条件筛选出来的列class

SELECT 
	c.name AS country,
    -- Count matches in each of the 3 seasons
	COUNT(CASE WHEN m.season = '2012/2013' THEN m.id END) AS matches_2012_2013,
	COUNT(CASE WHEN m.season = '2013/2014' THEN m.id END) AS matches_2013_2014,
	COUNT(CASE WHEN m.season = '2014/2015' THEN m.id END) AS matches_2014_2015
FROM country AS c
LEFT JOIN match AS m
ON c.id = m.country_id
-- Group by country name alias
GROUP BY country;

country	    matches_2012_2013	matches_2013_2014	matches_2014_2015
Portugal	  240	240	306
France	380	380	380
Scotland	228	228	228
Netherlands	306	306	306
Spain	380	380	380
Belgium	240	12	240
Italy	380	380	379
Germany	306	306	306
England	380	380	380
Switzerland	180	180	180
Poland	240	240	240
Showing 11 out of 11 rows

demo2date

case when + sum

SELECT 
	c.name AS country,
    -- Sum the total records in each season where the home team won
	SUM(CASE WHEN m.season = '2012/2013' AND m.home_goal > m.away_goal 
        THEN 1 ELSE 0 END) AS matches_2012_2013,
	SUM(CASE WHEN m.season = '2013/2014' AND m.home_goal > m.away_goal 
        THEN 1 ELSE 0 END) AS matches_2013_2014,
	SUM(CASE WHEN m.season = '2014/2015' AND m.home_goal > m.away_goal 
        THEN 1 ELSE 0 END) AS matches_2014_2015
FROM country AS c
LEFT JOIN match AS m
ON c.id = m.country_id
-- Group by country name alias
GROUP BY country;

country	matches_2012_2013	matches_2013_2014	matches_2014_2015
Portugal	103	108	137
France	170	168	181
Scotland	89	102	102
Netherlands	137	144	138
Spain	189	179	171
Belgium	102	6	106
Italy	177	181	152
Germany	130	145	145
England	166	179	172
Switzerland	84	82	76
Poland	97	110	114
Showing 11 out of 11 rows

忽然考虑能够作分箱和映射,就是映射和赋值

demo3

SELECT 
	c.name AS country,
    -- Sum the home wins, away wins, and ties in each country
    COUNT(CASE WHEN m.home_goal > m.away_goal THEN m.id 
        END) AS home_wins,
    COUNT(CASE WHEN m.home_goal < m.away_goal THEN m.id 
        END) AS away_wins,
    COUNT(CASE WHEN m.home_goal = m.away_goal THEN m.id 
        END) AS ties
FROM country AS c
LEFT JOIN matches AS m
ON c.id = m.country_id
GROUP BY country;

country	home_wins	away_wins	ties
Portugal	245	156	145
France	349	215	196
Scotland	204	158	94
Netherlands	282	173	157
Spain	350	233	177
Belgium	112	78	62
Italy	333	216	210
Germany	290	176	146
England	351	238	171
Switzerland	158	113	89
Poland	224	117	139
Showing 11 out of 11 rows

demo4

SELECT 
	c.name AS country,
    -- Round the percentage of tied games to 2 decimal points
	ROUND(AVG(CASE WHEN m.season='2013/2014' AND m.home_goal = m.away_goal THEN 1
			 WHEN m.season='2013/2014' AND m.home_goal != m.away_goal THEN 0
			 END),2) AS pct_ties_2013_2014,
	ROUND(AVG(CASE WHEN m.season='2014/2015' AND m.home_goal = m.away_goal THEN 1
			 WHEN m.season='2014/2015' AND m.home_goal != m.away_goal THEN 0
			 END),2) AS pct_ties_2014_2015
FROM country AS c
LEFT JOIN matches AS m
ON c.id = m.country_id
GROUP BY country;

country	pct_ties_2013_2014	pct_ties_2014_2015
Portugal	0.25	0.28
France	0.28	0.23
Scotland	0.22	0.19
Netherlands	0.27	0.24
Spain	0.23	0.24
Belgium	0.17	0.25
Italy	0.24	0.32
Germany	0.21	0.27
England	0.21	0.24
Switzerland	0.23	0.27
Poland	0.30	0.28
Showing 11 out of 11 rows

WHERE are the Subqueries?

子查询,或者说嵌套查询，这个很是的重要

一般在选择过滤信息以前对数据进行转化会须要用到子查询

where中的子查询

SELECT 
-- Select the average of home + away goals, multiplied by 3
	3 * AVG(home_goal + away_goal)
FROM matches_2013_2014;

顺序是先走where的子查询再走外层

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); 


date	home_goal	away_goal
2013-12-14	6	3
2014-03-22	3	6
2013-10-30	7	3

demo2

SELECT 
	-- Select the team long and short names
	team_long_name,
	team_short_name
FROM team
-- Exclude all values from the subquery
WHERE team_api_id NOT IN
     (SELECT DISTINCT hometeam_id FROM match);

demo3

SELECT
	-- Select the team long and short names
	team_long_name,
	team_short_name
FROM team
-- Filter for teams with 8 or more home goals
WHERE team_api_id in
	  (SELECT hometeam_ID 
       FROM match
       WHERE home_goal >= 8);

比较重要的是得知道怎么进行过滤

Subqueries in FROM

from以后的子查询

嵌套在from中的子查询

这个地方的子查询就至关于一个表，临时表，即表T。

也就是说，外面的select，其查询的内容就是括号内的子查询返回的数据集

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;

country_name	matches
Netherlands	1
Spain	4
Germany	1
England	3

demo2

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 c.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 subquery
-- Filter by total goals scored in the main query
WHERE total_goals >= 10;

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 and round the average total goals
    (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 m.season = '2013/2014'
GROUP BY l.name;

demo2

SELECT 
	-- Select the league name and average goals scored
	l.name AS league,
	ROUND(AVG(m.home_goal + m.away_goal),2) AS avg_goals,
    -- Subtract the overall average from the league average
	ROUND(AVG(m.home_goal + m.away_goal) - 
          (SELECT AVG(home_goal + away_goal)
           FROM match 
           WHERE season = '2013/2014'),2) AS diff
FROM league AS l
LEFT JOIN match AS m
ON l.country_id = m.country_id
-- Only include 2013/2014 results
WHERE m.season = '2013/2014'
GROUP BY l.name;

league	avg_goals	diff
Switzerland Super League	2.89	0.12
Poland Ekstraklasa	2.64	-0.13
Netherlands Eredivisie	3.20	0.43
Scotland Premier League	2.75	-0.02
France Ligue 1	2.46	-0.31
Spain LIGA BBVA	2.75	-0.02
Germany 1. Bundesliga	3.16	0.39
Italy Serie A	2.72	-0.04
Portugal Liga ZON Sagres	2.37	-0.40
England Premier League	2.77	0.00
Belgium Jupiler League

\SELECT 
	-- Select the stage and average goals from the subquery
	s.stage,
    ROUND(s.avg_goals,2) AS avg_goals
FROM 
	-- Select the stage and average goals in 2012/2013
	(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');

demo3

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');

stage	avg_goal	overall_avg
4	2.80	2.7726993865030675
10	2.96	2.7726993865030675
38	3.17	2.7726993865030675
6	2.78	2.7726993865030675
12	3.23	2.7726993865030675
36	2.90	2.7726993865030675
31	3.06	2.7726993865030675
30	2.87	2.7726993865030675
21	2.90	2.7726993865030675
3	2.83	2.7726993865030675
17	2.85	2.7726993865030675
20	2.96	2.7726993865030675
33	3.10	2.7726993865030675
27	2.80	2.7726993865030675
23	3.01	2.7726993865030675
8	3.09	2.7726993865030675
11	2.92	2.7726993865030675