将每次出现的 select 放入新列 (SQL)

Question

我有一个 SQL 数据库，其中包含一个由 4 列组成的简单 table。这些列是：“名称”、“时间”、“日期”和“月份”。我必须在视图中显示人员“A”在同一天的“时间”B 做了多少次。使用 select，我会将每次出现作为一个新行，例如

但我想要类似的东西

在 SQL 中可以吗？

Answer 1

如果你不知道每天的最大次数，那么使用group_concat():

select name, day, group_concat(time) as times
from t
group by name, day;

如果这样做，您可以使用条件聚合：

select name, day,
       max(case when seqnum = 1 then time end) as time_1,
       max(case when seqnum = 2 then time end) as time_2,
       max(case when seqnum = 3 then time end) as time_3,
       max(case when seqnum = 4 then time end) as time_4
from (select t.*,
             row_number() over (partition by name, date order by time) as seqnum
      from t
     ) t
group by name, day;

Answer 2

如果你使用 mysql 5.x 你可以使用一个枢轴 table

CREATE TABLE table1 (
  `Name` VARCHAR(1),
  `Time` VARCHAR(5),
  `Day` VARCHAR(4)
);

INSERT INTO table1
  (`Name`, `Time`, `Day`)
VALUES
  ('A', '11:00', '1/10'),
  ('A', '12:00', '1/10'),
  ('A', '13:00', '1/10'),
  ('A', '17:00', '1/10'),
    ('A', '10:00', '2/10'),
  ('A', '12:00', '2/10'),
  ('A', '14:00', '2/10'),
  ('A', '17:00', '2/10');

SELECT 
`Name`, 
IF(@date = `Day`,@rn:= @rn +1,@rn:= 1) rn
,`Time`
,@date := `Day` 'Day'
FROM table1, (SELECT @rn:= 0,@date := '')a
ORDER BY  `Name`,`Day`,`Time`

Name | rn | Time  | Day 
:--- | -: | :---- | :---
A    |  1 | 11:00 | 1/10
A    |  2 | 12:00 | 1/10
A    |  3 | 13:00 | 1/10
A    |  4 | 17:00 | 1/10
A    |  1 | 10:00 | 2/10
A    |  2 | 12:00 | 2/10
A    |  3 | 14:00 | 2/10
A    |  4 | 17:00 | 2/10

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
               CONCAT('MAX(IF(s.`rn` = "', `rn`,'", `Time`,"")) AS time_',rn)
              ) INTO @sql
FROM (SELECT 
`Name`, 
IF(@date = `Day`,@rn:= @rn +1,@rn:= 1) rn
,`Time`
,@date := `Day` 'Day'
FROM table1, (SELECT @rn:= 0,@date := '')a
ORDER BY  `Name`,`Day`,`Time`) t1;


SET @sql = CONCAT('SELECT `Name`,  ', @sql, ' ,`Day`
                  FROM (SELECT 
`Name`, 
IF(@date = `Day`,@rn:= @rn +1,@rn:= 1) rn
,`Time`
,@date := `Day` "Day"
FROM table1, (SELECT @rn:= 0,@date := "") a
ORDER BY  `Name`,`Day`,`Time`)  s
                 GROUP BY s.`Name`,s.`Day`
                ORDER BY s.`Name`,s.`Day`');
#SELECT @sql;
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;


Name | time_1 | time_2 | time_3 | time_4 | Day 
:--- | :----- | :----- | :----- | :----- | :---
A    | 11:00  | 12:00  | 13:00  | 17:00  | 1/10
A    | 10:00  | 12:00  | 14:00  | 17:00  | 2/10

db<>fiddle here

将每次出现的 select 放入新列 (SQL)

Put each occurence of a select in a new column (SQL)

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