RUNTIME error: DEFAULT not allowed in this context

[runebak]

I'm using PostgresSQL and I wanted to update a column to the default value if it was NULL.
Beam happily accepts both
(\r -> coalesce_ [just_ $current_ r.column] default_)
and
(\r -> if_ [isNothing_ (current_ r.column) then_ default_] (else_ $ current_ r.column))

But coalesce(r.column,DEFAULT) is not valid sql.
I need to supply the default manually.
I didn't find the proper way for this in beam, as the default is current_timestamp but the column is timstamptz in postgres corresponding to UTCTime in Haskell, but now_ in Beam only works for LocalTime .
I got around it with using coerce_ now_ instead,
but this doesn't feel right as it seems that GHC will happily coerce ANY beam type to one another...

(I have also used this coerce trick to get out of Maybe/Nullable when selecting only not null rows, haven't found a good way for this either.)

[runebak]

I don't see an easy way to enforce not allowing default_ in there, but I don't know about the internal of beam either. Not a critical thing, but I just thought you liked to know!

[LaurentRDC]

Thanks for the bug report! I will check it out as soon as I can.

I don't see an easy way to enforce not allowing default_ in there

The SQL AST is defined with a myriad of types and type classes, one of which might allow something it shouldn't. It might be as simple as tweaking one of those.

[LaurentRDC]

Reading a little bit more about coalesce and default in SQL, default can't be used as a function argument basically anywhere (at least in PostgreSQL).

[LaurentRDC]

I thought about this a little more. It looks like default_ shouldn't be a general QExpr. There are more layers to the SQL syntax.
Fixing this would be a major breaking change. For now, I'll update the documentation of coalesce_ and other functions. Happy to review pull requests on this topic.