Tom Lane wrote:
> Thomas Hallgren <thomas@tada.se> writes:
>
>> so why does it make a difference to use varchar instead of text?
>>
>
> It's a question of type resolution rules. text is the preferred string
> type so it "wins" in cross-type situations, in particular
> char_value = text_value
> will be interpreted as
> char_value::text text_eq text_value
> varchar is not only not a preferred type, it doesn't even have any
> comparison ops of its own (it depends on text's ops). Therefore given
> char_value = varchar_value
> the parser is faced with the alternative interpretations
> char_value::text text_eq varchar_value::text
> char_value char_eq varchar_value::char
> and it will prefer the latter because it has fewer casts.
> See
> http://www.postgresql.org/docs/8.1/static/typeconv.html
> particularly rules 10.2.3b and 3c. The upshot of all this
> is that a parameter specified as "text" dominates any comparison
> to other string datatypes, whereas one specified as "varchar"
> does not. Yeah, it's a bit grotty, but it gets the job done
> and it's not an area we're likely to change much.
>
> regards, tom lane
>
Hmm, OK. I checked my code and I don't use any specific type. Instead, I
use SPI_getargtypeid(ePlan, idx) on the prepared query and the
pgType->typinput function of the type that corresponds to the returned
oid. Perhaps the SPI_getargtypeid should return varchar for all text types?
Regards,
Thomas Hallgren