Question

我有以下数据：

ID | Image
1  |  10
2  |  11
3  |  
4  |
5  |

我想用加1之前的行值更新缺失值。

最终输出应为：

ID | Image
1  |  10
2  |  11
3  |  12
4  |  13
5  |  14

我在更新期间考虑过选择，但它不起作用。

UPDATE items AS item1
SET item1.image = (SELECT image 
                   FROM items AS item2 
                   WHERE item2.id < item1.id 
                   ORDER BY item2.id DESC LIMIT 1) + 1

Answer 1

使用用户变量尝试此解决方案，完整演示如下。

SQL：

-- data
create table items(ID int, Image int);
insert into items values
(1, 10),(2, NULL),(3, NULL),(4, NULL),(5, NULL);
SELECT * FROM items;

-- SQL needed
SET @i = 0;
UPDATE items
SET Image = (IF(Image IS NULL OR Image = '',
                @i:=@i+1,
                @i:=Image
                ));
SELECT * FROM items;

输出：

mysql> SELECT * FROM items;
+------+-------+
| ID   | Image |
+------+-------+
|    1 |    10 |
|    2 |  NULL |
|    3 |  NULL |
|    4 |  NULL |
|    5 |  NULL |
+------+-------+
5 rows in set (0.00 sec)

mysql>
mysql> SET @i = 0;
Query OK, 0 rows affected (0.00 sec)

mysql> UPDATE items
    -> SET Image = (IF(Image IS NULL OR Image = '',
    ->                 @i:=@i+1,
    ->                 @i:=Image
    ->                 ));
Query OK, 4 rows affected (0.00 sec)
Rows matched: 5  Changed: 4  Warnings: 0

mysql> SELECT * FROM items;
+------+-------+
| ID   | Image |
+------+-------+
|    1 |    10 |
|    2 |    11 |
|    3 |    12 |
|    4 |    13 |
|    5 |    14 |
+------+-------+
5 rows in set (0.00 sec)

Answer 2

您可以将UPDATE与JOIN一起使用到派生表中：

UPDATE Items AS i1
JOIN (
  SELECT ID, @n := @n + 1 AS Image
  FROM Items
  CROSS JOIN (SELECT @n := (SELECT MAX(Image) FROM Items)) AS v
  WHERE Image IS NULL
  ORDER BY ID
) AS i2 ON i1.ID = i2.ID
SET i1.Image = i2.Image;

派生表使用变量来计算Image s记录的NULL值。

Demo here

Answer 3

我有同样的问题，并且我对变量（@）使用简单的更新

update items,(select @n := 10) v set `Image`=@n:=@n+1 order by ID asc;

我希望这个查询有用：D

Answer 4

鉴于您提供的表格不是样本，我会像这样做一些简单易懂的事情：

Update items Set items.Image=items.id+9 WHERE items.Image is NULL;

天啊，我闻到了传入的投票！

基于前一行的MySQL更新列（同一列）

4 个答案: