我有一个survey_datas表包含这样的数据
survey_data_id | title
1 | Paul
3 | Anna
4 | Alan
另一个表project_playlist_indexes包含这样的数据
survey_id |survey_data_id | favorite
1 | 1 | 22.10
2 | 1 | 24.00
3 | 3 | 12.00
我想将survey_datas表与project_playlist_indexes表一起使用,以便project_playlist_indexes表中包含的与survey_datas表相同的survey_data_id的值应该是最喜欢的time1,最喜欢的时间2,…最喜欢的时间n,我想得到的结果表是像这样
survey_data_id |title | favorite_time1 | favorite_time2
1 | paul | 22.10 |24.00
3 | anna | 12.00 | null
4 | alan | null | null
目前我正在使用该查询
SELECT s.*,GROUP_CONCAT(pi.favorite) ,pi.*
FROM survey_datas s
LEFT JOIN project_playlist_indexes pi
ON pi.survey_data_id = s.survey_data_id
GROUP BY pi.survey_data_id
但最喜欢的值是进入一个字段,我希望它在不同的列中.我怎样才能做到这一点
最佳答案 您可以通过执行动态SQL查询来完成此操作.我所做的是,首先根据survey_data_id列给出一个行号.然后通过survey_data_id选择每个行编号项作为每个列组.不知道代码的效率如何.
询问
set @query = null;
select
group_concat(distinct
concat(
'max(case when `rn` = ',
`rn`,
' then `favorite` end) as `favorite', `rn` , '`'
)
) into @query
from (
select `survey_id`, `survey_data_id`, `favorite`, (
case `survey_data_id` when @curA
then @curRow := @curRow + 1
else @curRow := 1 and @curA := `survey_data_id` end
) as `rn`
from `project_playlist_indexes` t,
(select @curRow := 0, @curA := '') r
order by `survey_data_id`, `survey_data_id`
) t;
set @query = concat('select t2.`survey_data_id`, t2.`title`,',
@query,
' from (select `survey_id`, `survey_data_id`, `favorite`, (
case `survey_data_id` when @curA
then @curRow := @curRow + 1
else @curRow := 1 and @curA := `survey_data_id` end
) as `rn`
from `project_playlist_indexes` t,
(select @curRow := 0, @curA := '''') r
order by `survey_data_id`, `survey_data_id`) t1
right join `survey_datas` t2
on t1.survey_data_id = t2.`survey_data_id`
group by t1.`survey_data_id`
order by t2.`survey_data_id`;'
);
prepare stmt from @query;
execute stmt;
deallocate prepare stmt;