It would be great to add two more options on join conditions using question builder.
1 - Use different logic operators such as OR and change logic priorities using ()
Ex: (X=Y or Z=U) and R=E
2 - Add the use of fixed values on join conditions
Ex: X='TEST' and Z = Y
Add the TEST filtering on filtering will get the unmatched records of left/right joins out of the results while filtering on join conditions would display the unmatched records.
Hi @drconstantino
There's requests for more options:
https://github.com/metabase/metabase/issues/19443 - upvote by clicking 
on the first post
It is possible to use a static value on join by using a Custom Column. For strings, you would use concat.
I hit this same stumbling block and also discovered you can set a static value for a join condition using a custom column:
This works well enough but feels like we are creating technical debt. You also can't hide the custom column so have to explain to non-technical users of this report why there is suddenly a column full of the number 2 
I can see that the linked issues have been closed in the year since this thread started and fixed/static values in the join condition wasn't translated into the requirements.
@flamber I can start a new GitHub issue or comment on the existing one, what do you suggest?
(cc: @SamW )
