MYSQL：如何用前面的条目填充列中的空值？

我在工作中有一个程序，可以导出到CSV，但在最烦人的地方留下空白。我想在同一行上查看承运人和目的地，目前承运人位于目的地上方1行，如下所示：

我有一个如下所示的数据库： |钥匙|载体| |目的地| |-------------| |1 | HULL2 | || |2 | | C14A102| |3 | DONC1 | || |4 | | | D15A012|

我想要的是：

或者插入一个新列，其中包含来自carrier列的信息

抱歉，如果这让人困惑，我很难解释

---

James

假设列“key”可以通过这种方式信任，我将使用自联接进行更新，其中联接使用key=key+1，然后确保它只影响偶数行

UPDATE tablename as even_row JOIN tablename as odd_row 
ON even_row.Key = odd_row.Key + 1 
SET even_row.Carrier = odd_row.Carrier 
WHERE odd_row.Key % 2;

---

下面是一个解决方案，方法是克隆另一个表，然后将其删除：

CREATE TABLE t1(Key_id INT PRIMARY KEY, Carrier CHAR(20), Destination CHAR(20));
INSERT INTO t1 VALUES(1, 'HULL2', ''),(2,'','C14A102'),(3,'DONC1',''),(4,'','D15A012');

CREATE TABLE t2 LIKE t1;
INSERT INTO t2 SELECT * FROM t1;

SELECT * FROM t1;
UPDATE t1 SET Carrier = 
    (
    SELECT t2.Carrier
    FROM t2
    WHERE t2.Key_id < t1.Key_id AND t2.Carrier != ''
    ORDER BY t2.Key_id DESC
    LIMIT 1
    )
WHERE Carrier = '';
SELECT * FROM t1;

DROP TABLE t2;

输出：

mysql> SELECT * FROM t1;
+--------+---------+-------------+
| Key_id | Carrier | Destination |
+--------+---------+-------------+
|      1 | HULL2   |             |
|      2 |         | C14A102     |
|      3 | DONC1   |             |
|      4 |         | D15A012     |
+--------+---------+-------------+
4 rows in set (0.00 sec)

mysql> UPDATE t1 SET Carrier =
    -> (
    -> SELECT t2.Carrier
    -> FROM t2
    -> WHERE t2.Key_id < t1.Key_id AND t2.Carrier != ''
    -> ORDER BY t2.Key_id DESC
    -> LIMIT 1
    -> )
    -> WHERE Carrier = '';
Query OK, 2 rows affected (0.00 sec)
Rows matched: 2  Changed: 2  Warnings: 0

mysql> SELECT * FROM t1;
+--------+---------+-------------+
| Key_id | Carrier | Destination |
+--------+---------+-------------+
|      1 | HULL2   |             |
|      2 | HULL2   | C14A102     |
|      3 | DONC1   |             |
|      4 | DONC1   | D15A012     |
+--------+---------+-------------+
4 rows in set (0.00 sec)

---

解释它让我很困惑。。。你说出了我的话。你能给我们看一下预期的输出吗？对不起，蒂姆，我现在正试图修复！！你需要有一些字段来获得下一行。修复了帖子抱歉新帖子：谢谢你的回复，我在“where子句”中获得1054-未知列“cur_row.id”。我已经编辑了我的答案以使用你的列名，但我必须依靠你来了解我试图提出的建议，并根据您的情况进行适当调整。如果我的表中有1000多条不同运营商名称的线路，这会起作用吗？为什么不？只需用您自己的表名替换“t1”。你可以试一试@詹姆斯

mysql> SELECT * FROM t1;
+--------+---------+-------------+
| Key_id | Carrier | Destination |
+--------+---------+-------------+
|      1 | HULL2   |             |
|      2 |         | C14A102     |
|      3 | DONC1   |             |
|      4 |         | D15A012     |
+--------+---------+-------------+
4 rows in set (0.00 sec)

mysql> UPDATE t1 SET Carrier =
    -> (
    -> SELECT t2.Carrier
    -> FROM t2
    -> WHERE t2.Key_id < t1.Key_id AND t2.Carrier != ''
    -> ORDER BY t2.Key_id DESC
    -> LIMIT 1
    -> )
    -> WHERE Carrier = '';
Query OK, 2 rows affected (0.00 sec)
Rows matched: 2  Changed: 2  Warnings: 0

mysql> SELECT * FROM t1;
+--------+---------+-------------+
| Key_id | Carrier | Destination |
+--------+---------+-------------+
|      1 | HULL2   |             |
|      2 | HULL2   | C14A102     |
|      3 | DONC1   |             |
|      4 | DONC1   | D15A012     |
+--------+---------+-------------+
4 rows in set (0.00 sec)