如何在 Sql 中分组 table？

Question

我有以下 table, Tasks:

ID	Task	Type	Time_Taken
1	task1	type1	01h:00m
2	task1	type2	02h:00m
3	task2	type1	00h:30m
4	task2	type2	00h:30m
5	task3	type1	01h:00m
6	task3	type2	04h:00m

我想从 Tasks table 创建一个新的 table，应该是

Task	type1_time	type2_time
task1	01h:00m	02h:00m
task2	00h:30m	00h:30m
task3	01h:00m	04h:00m

你能帮我建立一个 sql 查询吗？

Answer 1

我假设此 SQL 查询是在 MySQL 数据库中处理的。请参考以下查询：

select Task, 
sum(if(Type='type1', Time_Taken,0)) as type1_time,
sum(if(Type='type2', Time_Taken,0)) as type2_time from Tasks 
group by Task

Answer 2

-- Solution INNER JOIN
SELECT type1.Task, type1.Time_Taken as 'type1_time', type2.Time_Taken as 'type2_time'
FROM Task type1 
INNER JOIN Task type2 on type1.Task = type2.Task
WHERE type1.Type = 'type1'
    AND type2.Type = 'type2';

--Solution GROUP_CONCAT
SELECT  
        t.Task,
        GROUP_CONCAT(IF(t.Type = "type1", t.Time_Taken, NULL)) AS 'type1_time',
        GROUP_CONCAT(IF(t.Type = "type2", t.Time_Taken, NULL)) AS 'type2_time'
FROM Task t
GROUP BY t.Task;

演示：https://paiza.io/projects/e/V9GtkWoJQAqewynjRXZ9-Q?theme=twilight

Answer 3

我的查询会给您预期的结果。演示 link：db-fiddle

SELECT Task, 
SEC_TO_TIME(sum(if(Type='type1', TIME_TO_SEC(Time_Taken),0))) as type1_time,
SEC_TO_TIME(sum(if(Type='type2', TIME_TO_SEC(Time_Taken),0))) as type2_time 
FROM Tasks 
GROUP BY Task

Answer 4

每个任务和类型都有一个条目。当你想按任务分组时，你可以使用 MIN 或 MAX 来访问类型的值，因为只有一个。

select
  task,
  min(case when type = 'type1' then time_taken end) as type1time,
  min(case when type = 'type2' then time_taken end) as type2time
from tasks
group by task
order by task;

这称为条件聚合，因为我们在条件上使用聚合函数（此处：当行与所需类型匹配时）。

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