Question

我的数据库中有一个表

+------+------+----------+
| id   | dept | location |
+------+------+----------+
|    1 | eee  | chennai  |
|    2 | ece  | chennai  |
|    3 | eee  | chennai  |
|    4 | ece  | chennai  |
|    5 | eee  | cbe      |
|    6 | ece  | trichy   |
|    7 | mech | madurai  |
+------+------+----------+

我需要在转置其中一列时计算id的数量。谁能建议我该查询以获取以下结果

+---------+------+-----+------+
| location| eee  | ece | mech |
+---------+------+-----+------+
| chennai | 2    | 2   |  0   |
| cbe     | 1    | 0   |  0   |
| trichy  | 0    | 1   |  0   |
| madurai | 0    | 0   |  1   |
+---------+------+-----+------+

谢谢您的帮助

Answer 1

select location as city,
       sum(dept = 'eee') as eee,
       sum(dept = 'ece') as ece,
       sum(dept = 'mech') as mech
from your_table
group by location

Answer 2

CREATE TABLE #TABLE1
    ([ID] INT, [DEPT] VARCHAR(4), [LOCATION] VARCHAR(7))
;

INSERT INTO #TABLE1
    ([ID], [DEPT], [LOCATION])
VALUES
    (1, 'EEE', 'CHENNAI'),
    (2, 'ECE', 'CHENNAI'),
    (3, 'EEE', 'CHENNAI'),
    (4, 'ECE', 'CHENNAI'),
    (5, 'EEE', 'CBE'),
    (6, 'ECE', 'TRICHY'),
    (7, 'MECH', 'MADURAI')
;


SELECT [LOCATION], COUNT(CASE WHEN DEPT = 'EEE' THEN [DEPT] END ) EEE ,
COUNT(CASE WHEN DEPT = 'ECE' THEN DEPT END )  ECE
,COUNT(CASE WHEN DEPT = 'MECH' THEN DEPT END ) MECH FROM #TABLE1
GROUP BY [LOCATION]

输出

LOCATION    EEE ECE MECH
CBE          1   0   0
CHENNAI      2   2   0
MADURAI      0   0   1
TRICHY       0   1   0

Answer 3

尝试与SUM一起CASE

create table test(id INT, dept VARCHAR(20), location VARCHAR(100))
insert into test values
(1,'eee','chennai'),
(2,'ece','chennai'),
(3,'eee','chennai'),
(4,'ece','chennai'),
(5,'eee','cbe'),
(6,'ece','trichy'),
(7,'mech','madurai')

SELECT 
    location AS city,
    SUM(CASE WHEN dept = 'eee' THEN 1 ELSE 0 END) eee,
    SUM(CASE WHEN dept = 'ece' THEN 1 ELSE 0 END) ece,
    SUM(CASE WHEN dept = 'mech' THEN 1 ELSE 0 END) mech
FROM test
GROUP BY location

输出

city    eee ece mech
cbe     1   0   0
chennai 2   2   0
madurai 0   0   1
trichy  0   1   0

Mysql计数或转置时的值计数

3 个答案: