SQL选择查询具有多个条件

I have a problem with a SQL select query, I can't figure out what it needs to be.

我有一个SQL select查询的问题，我不知道它需要什么。

This is what my items table look like:

这就是我的项目表:

| id |   i_id   |      last_seen       |   spot    |
----------------------------------------------------
| 1  |   ls100  | 2017-03-10 15:30:40  |  spot800  |
| 2  |   ls100  | 2017-03-10 16:20:15  |  spot753  |
| 3  |   ls200  | 2017-03-10 16:33:10  |  spot800  |
| 4  |   ls300  | 2017-03-10 15:30:40  |  spot800  |
| 5  |   ls300  | 2017-03-10 12:10:30  |  spot800  |
| 6  |   ls400  | 2017-03-10 10:30:10  |  spot800  |

This is what I'm trying to obtain:

这就是我想要得到的:

 | id |   i_id   |      last_seen       |   spot    |
 ----------------------------------------------------
 | 3  |   ls200  | 2017-03-10 16:33:10  |  spot800  |
 | 5  |   ls300  | 2017-03-10 12:10:30  |  spot800  |

So I need to have the rows where spot= 'spot800', last_seen = MAX(but only if the DateTime is the newest compared to all spots with the samei_id`), and at last the DateTime must be bigger than '2017-03-10 11:00:00'.

所以我需要有spot= 'spot800'、last_seen = MAX的行(但前提是DateTime与所有使用samei_id的点相比是最新的)，最后DateTime必须大于'2017-03-10 11:00:00'。

This is what I have so far:

这是我目前所拥有的:

SELECT * 
  FROM items
 WHERE spot = 'spot800' 
HAVING MAX(`last_seen`) 
   AND `last_seen` > '2017-03-10 11:00:00'

3 个解决方案

#1

E.g.:

例如:

DROP TABLE IF EXISTS my_table;

CREATE TABLE my_table
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,i_id   INT NOT NULL
,last_seen       DATETIME NOT NULL
,spot    INT NOT NULL
);

INSERT INTO my_table VALUES
(1,100,'2017-03-10 15:30:40',800),
(2,100,'2017-03-10 14:20:15',753),
(3,200,'2017-03-10 16:33:10',800),
(4,300,'2017-03-10 15:30:40',800),
(5,300,'2017-03-10 12:10:30',800),
(6,400,'2017-03-10 10:30:10',800);

    SELECT [DISTINCT] x.* 
      FROM my_table x
      LEFT
      JOIN my_table y
        ON y.i_id = x.i_id
       AND y.last_seen < x.last_seen
     WHERE x.last_seen > '2017-03-10 11:00:00' 
       AND x.spot = 800
       AND y.id IS NULL;
----+------+---------------------+------+
| id | i_id | last_seen           | spot |
+----+------+---------------------+------+
|  3 |  200 | 2017-03-10 16:33:10 |  800 |
|  5 |  300 | 2017-03-10 12:10:30 |  800 |
+----+------+---------------------+------+
2 rows in set (0.00 sec)

#2

Use MAX and GROUP BY.

使用MAX和GROUP BY。

SELECT id, i_id, MAX(last_seen), spot  
FROM items
WHERE spot = 'spot800'
AND last_seen > '2017-03-10 11:00:00'
GROUP BY id, i_id, spot

#3

There is several things wrng with your statement.

你的陈述中有几件事是错误的。

Firstly, HAVING must be accompanied with a GROUP BY clause, so it's not what you are looking for.

首先，必须有一组子句，所以这不是你想要的。

Also, MAX is an aggregate, not a boolean, function. That is, it cannot be used in filters, such as a where clause or a having clause. Also, if it did work, MAX would only return the entry that contains the time as '2017-03-10 16:33:10'. Not what you expected.

此外，MAX是一个集合，而不是布尔函数。也就是说，不能在筛选器中使用它，比如where子句或have子句。而且，如果它确实有效，MAX只会返回包含时间的条目，如“2017-03-10 16:33:10”。不是你的预期。

Try this instead:

试试这个:

SELECT * FROM items WHERE (spot='spot800' AND last_seen > '2017-03-10 11:00:00');

#1