动态重新排序 SQL Server 表中的列值

Question

我有一个用于用户技能的 SQL Server 表，每个用户的优先级顺序如下：

+----+------+----------+----------+
| ID | user | skill    | priority |
+----+------+----------+----------+
| 1  | foo  | swimming | 1        |
+----+------+----------+----------+
| 2  | foo  | running  | 2        |
+----+------+----------+----------+
| 3  | foo  | hunting  | 3        |
+----+------+----------+----------+
| 4  | boo  | swimming | 1        |
+----+------+----------+----------+
| 5  | moo  | swimming | 1        |
+----+------+----------+----------+
| 6  | moo  | running  | 2        |
+----+------+----------+----------+

当某个技能的优先级值发生更改时，我如何编写 SQL 代码来重新排序用户所有技能的优先级列值（整数）？

例如：对于用户“foo”，我将“游泳”技能的优先级从（1）更改为（2）；更新语句还必须以动态方式更改该用户所有其他技能的优先级。

因此，在该示例中，“游泳”的优先级为 (2) 而不是 (1)，跑步的优先级为 (1) 而不是 (2)，其他保持不变。

Answer 1

在这个答案中，我假设您想在 SQL 中执行此操作，而不是在 C# 中。基于该假设，单个事务中的这两条 SQL 语句将指定技能的优先级提高 1。

'Set @User to the required user and @Skill to the required skill.

'Decrease the priority of the user's skill above the specified skill.
UPDATE MyTable
SET    priority = priority + 1
WHERE  user = @User 
AND    priority = (SELECT priority - 1 
                   FROM MyTable 
                   WHERE user = @User
                   AND skill = @Skill)

'Increase the specified skill's priority.
UPDATE MyTable
SET    priority = priority - 1
WHERE  user = @User
AND    skill = @Skill
AND    priority > 1

以类似的方式，这两条SQL语句将指定技能提高到指定优先级。

'Set @User to the required user and @Skill to the required skill.
'Set @NewPriority to the new priority.

'Decrease the higher-prioritised skills.
UPDATE MyTable
SET    priority = priority + 1
WHERE  user = @User 
AND    priority >= @NewPriority 
AND    priority < (SELECT priority
                   FROM MyTable 
                   WHERE user = @User
                   AND skill = @Skill)

'Set the specified skill's priority as requested.
UPDATE MyTable
SET    priority = @NewPriority 
WHERE  user = @User
AND    skill = @Skill
AND    priority > 1

而这三个SQL语句移动指定技能到指定优先级。

'Set @User to the required user and @Skill to the required skill.
'Set @NewPriority to the new priority.

'Decrease the higher-prioritised skills to
'handle case where new priority is higher.
UPDATE MyTable
SET    priority = priority + 1
WHERE  user = @User 
AND    priority >= @NewPriority 
AND    priority < (SELECT priority
                   FROM MyTable 
                   WHERE user = @User
                   AND skill = @Skill)

'Increase the lower-prioritised skills to
'handle case where new priority is lower.
UPDATE MyTable
SET    priority = priority - 1
WHERE  user = @User 
AND    priority <= @NewPriority 
AND    priority > (SELECT priority
                   FROM MyTable 
                   WHERE user = @User
                   AND skill = @Skill)    

'Set the specified skill's priority as requested.
UPDATE MyTable
SET    priority = @NewPriority 
WHERE  user = @User
AND    skill = @Skill