Re: [Haskelldb-users] insertQuery and default values

[Bjorn B. <bri...@cs...>]

On Jul 12, 2006, at 3:02 PM, Matthias Radestock wrote:

>
> How can I insert rows into a table with some column values coming =20
> from a
> query and the rest being set to their defaults?
>
> insertQuery generates SQL of the form
>
>   INSERT INTO table (SELECT ...)
>
> This doesn't allow default values to be specified because a) the =20
> SELECT
> must produce as many columns as there are in the table, b) it is =20
> illegal
> to write something like 'SELECT DEFAULT,..'.
>
> By contrast
>
>   INSERT INTO table(column,...) (SELECT ...)
>
> will give default values to all the columns that do not appear in the
> column list. However, from my experimenting and looking at the code it
> appears that there is currently no way to construct such a query.
>
> Would it be possible to add this? I suspect one difficulty might be
> expressing the record typing constraints required to make this =20
> operation
> safe.

HaskellDB's support for using default values is not very good. I =20
think that we would need a subtyping relation on records to implement =20=

this properly.

You will find that there are more things missing, like left joins. I =20
usually just fake whatever is missing using Haskell code, but that is =20=

of course less efficient.

I am starting to think that HaskellDB needs a serious overhaul to fix =20=

problems like this, and address back-end incompatibilities. I just =20
need to find the time to do it.

/Bj=F6rn