Dynamically reorder column values in a SQL Server table - tsql

Question

I have a SQL Server table for user skills with priority order for each user as this:
+----+------+----------+----------+
| 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 |
+----+------+----------+----------+
How can I write SQL code to re-order the priority column values (an integer) for all skills for a user when the priority value is changed for one of the skills?
For example: for user "foo" I will change the priority of the skill "swimming" from (1) to (2); the update statement must also change the priority for all other skills for that user, in a dynamic way.
So in that example "swimming" will be priority (2) instead of (1), running will be (1) instead of (2), and the others will remain the same.

Answer 1

In this answer I'm assuming that you want to do this in SQL, not in C#. Based on that assumption, these two SQL statements inside a single transaction increase the priority of the specified skill by 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
In a similar fashion, these two SQL statements increase the specified skill to the specified priority.
'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
And these three SQL statements move the specified skill to the specified priority.
'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