MySQL IF语句即时更改值？

Question

I'm not even sure if this is quite possible to do with MySQL, but I hope it is.

OK so i have this SQL command

SELECT * FROM table WHERE $WhereCondition ORDER BY ListStyle

As an example of the data in the ListStyle I might have

2000 3000 3700 3800

What I'm hoping to do is use some kind of if statement in the SQL that will allow me to check other fields in a result row so that I can change the value of the ListStyle before I use that in the page to order it appropriately.

So for instance I have fields a, b and c. Now if a and b are NOT empty and c = 100 and the ListStyle = 3700, I want to change the value of ListStyle to 3699 so that when I print out a result loop, rows that match the condition ( a != '', b != '', c = 100 and ListStyle = 3700) will then be shown above the rows that have the ListStyle of 3700

I can't simply edit the data in the database, even though that would be an easy solution. The data has to stay as it is.

I originally tried doing this in php. While its easy enough to change the value of the ListStyle using if statements, I don't know of an easy way to then actually order my results without sticking everything into an array and then sorting through it. I really don't want to do that as it would mean re-writing a lot of code, which is why I'm hoping this is all possible to do in MySQL.

Can anyone help with this?

Answer 1

try something like:

SELECT * FROM table_name WHERE $WhereCondition ORDER BY CASE 
        WHEN ( a = 0, b = 0, c = 100 and ListStyle = 3700)  THEN 1
        WHEN ( a = 10, b = 20, c = 200 and ListStyle = 3400) THEN 2
        ELSE 10
    END

Answer 2

You can use IF or CASE inside the ORDER BY statement like

...
ORDER BY
  IF(condition1, then_value, else_value)

Answer 3

How about this?

SELECT a,b,c, IF($condition, 3700, 3699) AS order WHERE $whereCondition ORDER BY order

Expressing $condition in MySQL might be tedious, but I think it's possible.

Answer 4

你可以使用触发器