Question

我有2个MySQL表，我需要加入并作为派生表进行访问。

一些虚拟行的基本示例：

CREATE DATABASE Test;
USE Test;

CREATE TABLE TableOne(
    Id INT auto_increment NOT NULL,
    SomeField FLOAT,
    Timestamp DATETIME,
        PRIMARY KEY(Id)
);

CREATE TABLE TableTwo(
    Id INT auto_increment NOT NULL,
    SomeField FLOAT,
    Timestamp DATETIME,
        PRIMARY KEY(Id)
);

INSERT INTO TableOne
    (Timestamp, SomeField)
VALUES
    ('2017-06-30 23:30:00', RAND()),
    ('2017-06-30 23:45:00', RAND()),
    ('2017-07-01 00:00:00', RAND()),
    ('2017-07-01 00:15:00', RAND()),
    ('2017-07-01 00:30:00', RAND()),
    ('2017-07-01 00:45:00', RAND()),
    ('2017-07-01 01:00:00', RAND()),    
    ('2017-07-01 01:15:00', RAND()),    
    ('2017-07-01 01:30:00', RAND());    


INSERT INTO TableTwo
    (Timestamp, SomeField)
VALUES
    ('2017-06-30 23:30:00', RAND()),
    ('2017-06-30 23:40:00', RAND()),
    ('2017-06-30 23:50:00', RAND()),
    ('2017-07-01 00:00:00', RAND()),
    ('2017-07-01 00:10:00', RAND()),
    ('2017-07-01 00:20:00', RAND()),
    ('2017-07-01 00:30:00', RAND()),
    ('2017-07-01 00:40:00', RAND()),
    ('2017-07-01 00:50:00', RAND()),
    ('2017-07-01 01:00:00', RAND()),
    ('2017-07-01 01:10:00', RAND()),
    ('2017-07-01 01:20:00', RAND()),
    ('2017-07-01 01:30:00', RAND());

要阅读表格，我正在使用：

SELECT
    SomeField,
    Timestamp
FROM
    (
        SELECT
            SomeField,
            Timestamp
        FROM
            TableOne

        UNION

        SELECT
            SomeField,
            Timestamp
        FROM
            TableTwo    
    ) d1
WHERE
    d1.Timestamp BETWEEN '2017-07-01 00:00:00' AND '2017-07-01 01:00:00'
ORDER BY
    d1.Timestamp;

此查询返回以下表格：

+------------+---------------------+
| SomeField  | Timestamp           |
+------------+---------------------+
|   0.380433 | 2017-07-01 00:00:00 |
| 0.00938889 | 2017-07-01 00:00:00 |
|   0.963191 | 2017-07-01 00:10:00 |
|   0.290852 | 2017-07-01 00:15:00 |
|   0.674658 | 2017-07-01 00:20:00 |
|   0.483715 | 2017-07-01 00:30:00 |
|   0.426091 | 2017-07-01 00:30:00 |
|   0.394602 | 2017-07-01 00:40:00 |
|   0.257901 | 2017-07-01 00:45:00 |
|   0.521865 | 2017-07-01 00:50:00 |
|   0.425519 | 2017-07-01 01:00:00 |
|  0.0112322 | 2017-07-01 01:00:00 |
+------------+---------------------+
12 rows in set (0.00 sec)

Test.TableOne中的时间戳（例如）每十五分钟一次。

Test.TableTwo中的时间戳（例如）每十分钟一次。

我希望能够做的是使用＆＃39; SomeField＆＃39;返回带有所有时间戳的派生表。列显示相应DATETIME的Null。

示例（使用上表）将如下所示：

+------------+---------------------+
| SomeField  | Timestamp           |
+------------+---------------------+
|   0.380433 | 2017-07-01 00:00:00 |
| 0.00938889 | 2017-07-01 00:00:00 |
|   0.963191 | 2017-07-01 00:10:00 |
|   NULL     | 2017-07-01 00:10:00 |
|   0.290852 | 2017-07-01 00:15:00 |
|   NULL     | 2017-07-01 00:15:00 |
|   0.674658 | 2017-07-01 00:20:00 |
|   NULL     | 2017-07-01 00:20:00 |
|   0.483715 | 2017-07-01 00:30:00 |
|   0.426091 | 2017-07-01 00:30:00 |
|   0.394602 | 2017-07-01 00:40:00 |
|   NULL     | 2017-07-01 00:40:00 |
|   0.257901 | 2017-07-01 00:45:00 |
|   NULL     | 2017-07-01 00:45:00 |
|   0.521865 | 2017-07-01 00:50:00 |
|   NULL     | 2017-07-01 00:50:00 |
|   0.425519 | 2017-07-01 01:00:00 |
|  0.0112322 | 2017-07-01 01:00:00 |
+------------+---------------------+
18 rows in set (0.00 sec)

我尝试了很多不同的JOIN来实现这一点而没有运气。

任何帮助将不胜感激。感谢。

Answer 1

如果按时间戳只使用一行，并且每个表中的值使用两个列，则可以使用较小的查询。

但是，如果您确实需要输出，就像您要求的那样，您需要模拟两个完整的外连接并将它们联合起来：

select * from (
           select t1.SomeField,Timestamp from TableOne t1 left join TableTwo t2 using (Timestamp) union all 
           select t2.SomeField,Timestamp from TableOne t1 left join TableTwo t2 using (Timestamp) union all
           select t1.SomeField,Timestamp from TableOne t1 right join TableTwo t2 using (Timestamp) union all 
           select t2.SomeField,Timestamp from TableOne t1 right join TableTwo t2 using (Timestamp)

          ) tt where tt.Timestamp BETWEEN '2017-07-01 00:00:00' AND '2017-07-01 01:00:00' order by Timestamp

MySQL为不存在的记录返回null

1 个答案: