Question

我有一个像这样的主表

customer_id  Customer_name
1             A
2             B
3             C
4             D

我有多个用户活动表。我只给出了2个这样的表的例子，但是有20个这样的表

表1：

customer_id     activity_date   No_of_likes
2                1/1/16          2
3                1/1/16          3
2                2/1/16          5
2                1/1/16          1

表2：

customer_id     activity_date   No_of_comments
2                1/1/16          1
4                5/1/16          7
2                6/1/16          2

这是我需要的最后一张桌子。我没有主日历表，我不确定如何加入以获得以下输出

customer_id     activity_name   activity_date    quantity
1                -                  -              -
2               Likes             1/1/16            3
2               Likes             2/1/16            5
2               Comments          1/1/16            1
2               Comments          6/1/16            2
3               Likes             1/1/16            3
4               Comments          5/1/16            7

我还需要这样的输出。我认为合并解决了上述问题，但我不知道如何做到以下

  customer_id      activity_date    like_quantity    comment_activity 
     1                 -                -                     - 
     2                1/1/16            3                     1 
     2                2/1/16            5                     - 
     2                6/1/16            -                     2 
     3                1/1/16            3                     - 
     4                5/1/16            -                     7

希望我很清楚。请帮助我查询有关此连接的SQL查询

Answer 1

你可以试试这个：

使用UNION和LEFT JOIN即可完成此任务。

SELECT 
  your_master_table.customer_id,
  COALESCE(t.activity_name,'-') AS activity_name,
  COALESCE(t.activity_date,'-') AS activity_date,
  COALESCE(t.quantity,'-') AS quantity
FROM your_master_table

LEFT JOIN 
(
    SELECT 
    customer_id,
    activity_date,
    No_of_likes AS quantity,
    'Likes' AS activity_name
    FROM TABLE_1

    UNION 

    SELECT 
    customer_id,
    activity_date,
    No_of_comments AS quantity,
    'Comments' AS activity_name
    FROM TABLE_2

) AS t
ON your_master_table.customer_id = t.customer_id
ORDER BY your_master_table.customer_id;

SQL FIDDLE DEMO

在您的示例输入上运行上述查询，您将获得以下输出：

<强>输出：

| customer_id | activity_name | activity_date | quantity |
|-------------|---------------|---------------|----------|
|           1 |             - |             - |        - |
|           2 |      Comments |    2016-01-01 |        1 |
|           2 |      Comments |    2016-01-06 |        2 |
|           2 |         Likes |    2016-01-01 |        2 |
|           2 |         Likes |    2016-01-02 |        5 |
|           2 |         Likes |    2016-01-01 |        1 |
|           3 |         Likes |    2016-01-01 |        3 |
|           4 |      Comments |    2016-01-05 |        7 |

修改

根据您的要求变更

SELECT your_master_table.customer_id, COALESCE(DATE_FORMAT(t.activity_date,'%d/%m/%y'),'-') AS activity_date, COALESCE(SUM(CASE WHEN t.activity_name = 'Likes' THEN t.quantity END),'-') AS like_quantity, COALESCE(SUM(CASE WHEN t.activity_name = 'Comments' THEN t.quantity END),'-') AS comment_activity FROM your_master_table LEFT JOIN ( SELECT customer_id, activity_date, No_of_likes AS quantity, 'Likes' AS activity_name FROM TABLE_1 UNION SELECT customer_id, activity_date, No_of_comments AS quantity, 'Comments' AS activity_name FROM TABLE_2 ) AS t ON your_master_table.customer_id = t.customer_id GROUP BY your_master_table.customer_id,t.activity_date ORDER BY your_master_table.customer_id;

SQL FIDDLE DEMO

连接具有多个日期的多个表

1 个答案: