我在使用SQL查询时遇到麻烦。我有两个桌子。
我的第一张桌子：
+------------+-------------+---------------+
| id_mission | Some column | Other column |
+------------+-------------+---------------+
| 1 | ... | ... |
| 2 | ... | ... |
+------------+-------------+---------------+
我的第二张桌子：
+------------+-------------+---------+
| id_mission | id_category | points |
+------------+-------------+---------+
| 1 | 1 | 3 |
| 1 | 2 | 4 |
| 1 | 3 | 4 |
| 1 | 4 | 8 |
| 2 | 1 | -4 |
| 2 | 2 | 3 |
| 2 | 3 | 1 |
| 2 | 4 | -7 |
+------------+-------------+---------+
我想在SELECT请求中得到这种结果
+------------+-------------+--------------+---------------+----------------+
| id_mission | Some column | Other column | id_category 1 | id_category X |
+------------+-------------+--------------+---------------+----------------+
| 1 | ... | ... | ... | ... |
| 2 | ... | ... | ... | ... |
+------------+-------------+--------------+---------------+----------------+
我已经在前两列中尝试过此方法，但是它不起作用，我也尝试过GROUP_CONCAT，它有效，但这不是我想要的结果。
SELECT m.id_mission ,mc.id_category 1,mc1.id_category 2
from mission m
left join mission_category mc on m.id_mission = mc.id_mission
left join mission_category mc1 on m.id_mission = mc1.id_mission
有人可以帮我吗？
答案 0 :(得分：2)
您可以使用条件聚合。假设您想按类别旋转fun findDate(dayOfMonth: Int): LocalDate {
val now = LocalDate.now()
val currentDayOfMonth = now.getDayOfMonth()
if (currentDayOfMonth <= dayOfMonth) {
// use the current month with the given day of month
return now.withDayOfMonth(dayOfMonth)
// subtract a day (will change the month when dayOfMonth == 1)
.minusDays(1)
// and add a month
.plusMonths(1)
} else {
// otherwise just take the current month with the given day of month
return now.withDayOfMonth(dayOfMonth)
// and subtract a day
.minusDays(1)
}
}
值：
points这假定select
t1.*,
max(case when t2.id_category = 1 then points end) category_1,
max(case when t2.id_category = 2 then points end) category_2,
max(case when t2.id_category = 3 then points end) category_3
from t1
inner join t2 on t2.id_mission = t1.id_mission
group by t1.id_mission
是id_mission的主键（否则，您需要枚举t1和select子句中想要的列）。 / p>