MySQL案例语句透视问题

请建议将表1转换为表2

Actual Result:  
      User_id type   created_at
        1        1     2015-02-01
        1        2     2015-03-10
        1        3     2015-04-22 



Expected Result:

    user_id, type1_date, type2_date, type3_date

查询：

select user_id, 
       case when type=1 then created_at end as Type1,
       case when type=2 then created_at end as Type2,
       case when type=3 then created_at end as Type3 
from t1

试试这个

SELECT User_id,
     MAX(CASE WHEN type = 1 THEN created_at END) AS type1_date,
     MAX(CASE WHEN type = 2 THEN created_at END) AS type2_date,
     MAX(CASE WHEN type = 3 THEN created_at END) AS type3_date
FROM {your_table}
GROUP BY User_id

---

查询中的问题：

select user_id, 
       case when type=1 then created_at end as Type1,
       case when type=2 then created_at end as Type2,
       case when type=3 then created_at end as Type3 
from t1

您尚未使用聚合函数

MAX（）

。因此，查询不会删除值为

NULL

的字段

解决方案：

select user_id, 
       case when type=1 then created_at end as Type1,
       case when type=2 then created_at end as Type2,
       case when type=3 then created_at end as Type3 
from t1

使用

MAX（）

和

分组依据

SELECT user_id,
       MAX(CASE WHEN type=1 THEN created_at END) AS type1_date,
       MAX(CASE WHEN type=2 THEN created_at END) AS type2_date,
       MAX(CASE WHEN type=3 THEN created_at END) AS type3_date
FROM t1
GROUP BY user_id

---

如果类型列的值有限制，这是pivot的另一种选择：

您尝试了什么吗？是的，我为每个类型添加了大小写，但它给出了3行，但我在1中查找row@jacob53：您的表中将有多少类型？选择用户\u id，当type=1时，选择case，然后在末尾创建为Type1，当type=2时，案例在末尾创建为Type2，当type=3时，案例在末尾从t1创建为Type3