[英]Select dynamic row values as column names, in specific order
继续我的上一个问题 :我必须将动态行值用作列,但是列的顺序需要具体。 如果看下面的示例,我必须按start_time升序对所选列进行排序。
例如:
+---------+------------+-------------------+----------+---------------+---------------+
| exec_id | project_id | flow_id | job_id | start_time | end_time |
+---------+------------+-------------------+----------+---------------+---------------+
| 10919 | 16 | my_flow_cleanup | init | 10 | 15 |
| 10919 | 16 | my_flow_cleanup | job_id_1 | 30 | 40 |
| 10919 | 16 | my_flow_cleanup | job_id_2 | 40 | 50 |
| 10919 | 16 | my_flow_cleanup | job_id_3 | 20 | 25 |
+---------+------------+-------------------+----------+---------------+---------------+
从上一个问题开始:
SET @sql = NULL;
SELECT GROUP_CONCAT(DISTINCT
CONCAT('MAX(CASE WHEN job_id = ''',
job_id,
''' THEN start_time END) `',
job_id,
'_start`',
',',
'MAX(CASE WHEN job_id = ''',
job_id,
''' THEN end_time END) `',
job_id,
'_end`'
)
)
INTO @sql
FROM t;
SET @sql = CONCAT('SELECT exec_id, ', @sql, '
FROM t
GROUP BY exec_id');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
上面的查询将返回以下结果:
exec_id init_start init_end job_id_1_start job_id_1_end job_id_2_start job_id_2_end job_id_3_start job_id_3_end
10919 10 15 30 40 40 50 20 25
但是我需要:
exec_id init_start init_end job_id_3_start job_id_3_end job_id_1_start job_id_1_end job_id_2_start job_id_2_end
10919 10 15 20 25 30 40 40 50
请注意,现在根据start_time更改了列的顺序。
我试图使用temporary tables
和views
来做到这一点,我认为这将非常容易。 不幸的是,我没有创建表/创建视图的权限。 没有临时表和视图,有没有办法实现这一目标?
您可以通过在GROUP_CONCAT
函数中添加ORDER BY start_time ASC
来完成此操作
SET @sql = NULL;
SELECT GROUP_CONCAT(DISTINCT
CONCAT('MAX(CASE WHEN job_id = ''',
job_id,
''' THEN start_time END) `',
job_id,
'_start`',
',',
'MAX(CASE WHEN job_id = ''',
job_id,
''' THEN end_time END) `',
job_id,
'_end`'
)
ORDER BY start_time ASC
)
INTO @sql
FROM t;
SET @sql = CONCAT('SELECT exec_id, ', @sql, '
FROM t
GROUP BY exec_id');
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;
Fiddle Demo
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