Re: Recursive CTE and collation

On 14/06/2019 15:39, Tom Lane wrote:
> =?UTF-8?Q?S=c3=a9bastien_Lardi=c3=a8re?=  writes:
>> While playing with the query showed here :
>> https://fluca1978.github.io/2019/06/12/PartitioningCTE.html
>> I've seen something strange with v12 (actually compiled after
>> f43608bda2111a1fda514d1bed4df313ee2bbec3 so more recent than beta1) :
>> psql: ERROR:  recursive query "inheritance_tree" column 3 has collation
>> "default" in non-recursive term but collation "C" overall
>> LINE 4:             , NULL::text AS table_parent_name
>>                       ^
>> HINT:  Use the COLLATE clause to set the collation of the non-recursive
>> term.
> Yeah.  Your query is really wrong as it stands, because it's trying
> to union "NULL::text" with a column of type "name".  

Indeed, ::text is wrong,

> That accidentally
> works in previous releases, but as of v12, "name" has acquired
> collatability, and the recursive-union rules don't allow papering that
> over.


Good to know,


> I notice that it does work in a regular union:
>
> regression=# select null::text union select null::name collate "C";
>  text 
> ------
>  
> (1 row)
>
> but I believe that recursive union is intentionally stricter.
>
>> It work correctly with 11, and with 12, we can workaround by adding
>> COLLATE "C" after NULL::text, so I don't know if it's a bug or a new
>> feature, but it break things, at least.
> I'd suggest using "NULL::name" instead.

yes, thanks,

-- 

Sébastien