I need to `GROUP BY item_id` and check if `user_id` in any of those matches a variable. If so, I want it to = 1, if not 0.

for example, imagine table like this:

```
item_id, user_id
1         1
1         3
2         4
2         1
2         7
2         3
3         4
3         6
4         8
4         1
5         3

IF (user_id = 3,1,0) AS match,

```

Want my Query to come back as

```
item_id, match
1        1 
2        1
3        0
4        0
5        1

```

Where "1" all occurrences of user\_id 3 in an item\_id group.