On 2/22/16 5:13 PM, Alvaro Herrera wrote:
Jim Nasby wrote:
On 2/22/16 11:47 AM, Alvaro Herrera wrote:
Pavel Stehule wrote:

The design of the "format" function is not closed. Try to send prototype
and patch. The possibility to do PostgreSQL customization was strong reason
why we didn't implemented "sprintf" and we implemented "format".

Probably not terribly useful here, but for the DDL-deparse patch I came
up with a syntax to format JSON objects, which used %-escapes; each
escaped element corresponds to a string literal, or to an object.  So
you'd have %{table}D where the "table" element in the JSON object could
be a simple string which is expanded verbatim (plus quoting if
necessary), or it could be a JSON object with something like { schema =>
"public", name => "students" }, where each element is expanded and
quoted as necessary; if the "schema" is null or it doesn't exist, it
expands only the name, obviously omitting the dot.

Where did the "D" in "%{table}D" come from?

The I in %{foo}I was for "identifier" (of course) and I *think* the D
was for "double identifiers" (that is, qualified).  I expanded the idea
afterwards to allow for a third name for things like
catalog.schema.name, so I guess it's a misnomer already.

It's not released code yet.  You can see an example here
just scroll down a few hundred lines to about 7/16ths of the page (yes,

(One thing I had to come up with was processing of arrays, which you
also see in that example JSON -- it's the specifiers that have a colon
inside the {}.  The part after the colon is used as separator between
the array elements, and each element is expanded separately.)

Ahh, very interesting.

Something that would probably be helpful for these kind of things is if we had a set of complex types available that represented things like the arguments to a function. Something like (parameter_mode enum(IN, OUT, INOUT), parameter_name name, parameter_type regtype, parameter_default text). A function might be represented by (function_schema name, function_name name, function_parameters ..., function_language, function_options, function_body).

In any case, having anything along these lines in core would be useful, assuming that the individual facility was exposed as well (as opposed to only being available inside an event trigger).
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com

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