Regards on this result set from this Query :

Select * from [My_Table]

FK_id| name   | code  |
___________________
1 | first  | 21500 |
___________________
1 | first  | 0     |
___________________
2 | second | 21500 |
___________________
4 | four   | 21500 |
___________________
4 | four   | 42000 |
___________________
4 | four   | 0     |
___________________
5 | fifth  | 0     |
___________________
5 | fifth  | 42000 |
___________________
6 | six  | 0       |
___________________

I need to select lines (distinct Fk_ID) where those condition are satisfied :

If code is different to 0 we take the one with the code we want(its a parameter to the query) If there is no line equal to this parameter we take the one with 0.

This is what I need :

If code = 21500 :

Fk_id| name   | code  |
___________________
1 | first  | 21500 |
___________________
2 | second | 21500 |
___________________
4 | four   | 21500 |
___________________
5 | fifth  | 0     |
___________________
6 | six  | 0       |
___________________

If code = 42000 :

Fk_id| name   | code  |
___________________
1 | first  | 0     |
___________________
4 | four   | 42000 |
___________________
5 | fifth  | 42000 |
___________________
6 | six  | 0       |
___________________

I need to have the SQL queries first, no need to have doctrine Query builder.

解决方案

I added an id column to ease the edition with PHPMyAdmin but it doesn't play any role here.

If code = 21500 :

SELECT * FROM `test`
WHERE (`code` = 21500 OR `code` = 0)
GROUP BY `name`
ORDER BY `FK_id`

Demo at SQL Fiddle.

Result:

| id | FK_id |   name |  code |
|----|-------|--------|-------|
|  1 |     1 |  first | 21500 |
|  3 |     2 | second | 21500 |
|  4 |     4 |   four | 21500 |
|  7 |     5 |  fifth |     0 |
|  9 |     6 |    six |     0 |

If code = 42000 :

SELECT *, MAX(code) FROM `test`
WHERE (`code` = 42000 OR `code` = 0)
GROUP BY `name`
ORDER BY `FK_id`

Demo at SQL Fiddle.

Result:

| id | FK_id |  name |  code | MAX(code) |
|----|-------|-------|-------|-----------|
|  2 |     1 | first |     0 |         0 |
|  5 |     4 |  four | 42000 |     42000 |
|  7 |     5 | fifth |     0 |     42000 |
|  9 |     6 |   six |     0 |         0 |

I use MAX() in order to get 42000 and not 0 on the first line of results.

In both queries you can replace GROUP BY `name` with GROUP BY `FK_id`.