Re: proposal: doc: simplify examples of dynamic SQL
| От | David G. Johnston |
|---|---|
| Тема | Re: proposal: doc: simplify examples of dynamic SQL |
| Дата | |
| Msg-id | CAKFQuwY+40SPc33F-BkL3-8LAcwMvbn0kpxZOCF2MU8XpXOJwQ@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: proposal: doc: simplify examples of dynamic SQL (Bruce Momjian <bruce@momjian.us>) |
| Ответы |
Re: proposal: doc: simplify examples of dynamic SQL
|
| Список | pgsql-hackers |
On Thu, Mar 19, 2015 at 04:01:32PM -0700, David G. Johnston wrote:
> Prefacing it with: "You may also see the following syntax in the wild since
> format was only recently introduced."
>
> may solve your lack of reason for inclusion.
Uh, the problem with that is we are not going to revisit this when
format isn't "recently introduced". I think script writers naturally
think of query construction using string concatenation first, so showing
it first seems fine.
+1
There are other places later in the docs where we explain all the quote*
functions and show examples of query construction using string
concatenation, but I am not sure how we can remove those.
Can you be more specific?
On a related note:
"If you are dealing with values that might be null, you should usually use quote_nullable in place of quote_literal."
Its unclear why, aside from semantic uncleanliness, someone would use quote_literal given its identical behavior for non-null values and inferior behavior which passed NULL. The function table for the two could maybe be more clear since quote_nullable(NULL) returns a string representation of NULL without any quotes while quote_literal(NULL) returns an actual NULL that ultimately poisons the string concatenation that these functions are used with.
<reads some more>
The differences between the actual null and the string NULL are strictly in capitalization - which is not consistent even within the table. concat_ws states "NULL arguments are ignored" and so represents actual null with all-caps which is string NULL in the quote_* descriptions. Having read 40.5.4 and example 40-1 the difference is clear and obvious so maybe what is in the table is sufficient for this topic.
I would suggest adding a comment to quote_ident and quote_nullable that corresponding format codes are %I and %L. Obviously there is no "quote_" function to correspond with %S. There is likewise nor corresponding format code for quote_literal since quote_nullable is superior in every way (that I can tell at least).
David J.
В списке pgsql-hackers по дате отправления: