MySQL高级UPDATE查询

Question

我想将图像设置为专辑的封面,我是通过在do-while循环中的无线电输入中选择它来实现的.我已经在图像表中放入了一个名为is_cover的字段,如果图像设置为封面则为1,否则为0.

<input type="radio" name="cover" value="<?php echo $row_images['image_id']; ?>" <?php if($row_images['is_cover'] == 1){ echo "checked=\"checked\""; } ?> />

我的问题是如何执行更新查询,将所有图像is_cover字段设置为0,并且只有所选图像的值为1.

我想说的是我怎样才能做到这一点:

$is_cover = $_POST['cover'];
$query = "
    UPDATE images 
    SET is_cover = 1 
    WHERE image_id = {$is_cover} 
          AND SET is_cover = 0 
    WHERE image_id <> {$is_cover}
";

Answer 1

这应该是你的诀窍:

UPDATE images SET is_cover = CASE WHEN image_id = {$is_cover} THEN 1 ELSE 0 END;

从我的测试:

mysql> select * from first;
+------+-------+
| id   | title |
+------+-------+
|    1 | aaaa  |
|    2 | bbbb  |
|    3 | cccc  |
|    4 | NULL  |
|    6 | ffff  |
+------+-------+
5 rows in set (0.01 sec)

mysql> update first set title = case when id > 4 then 'gggg' else title end;
Query OK, 1 row affected (0.01 sec)
Rows matched: 5  Changed: 1  Warnings: 0

mysql> select * from first;
+------+-------+
| id   | title |
+------+-------+
|    1 | aaaa  |
|    2 | bbbb  |
|    3 | cccc  |
|    4 | NULL  |
|    6 | gggg  |
+------+-------+
5 rows in set (0.00 sec)