Horton

Re: [HACKERS] [PATCH] Generic type subscripting

Pavel Stehule <pavel.stehule@gmail.com>

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From: Pavel Stehule <pavel.stehule@gmail.com>
To: Dmitry Dolgov <9erthalion6@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Oleksandr Shulgin <oleksandr.shulgin@zalando.de>, Artur Zakirov <a.zakirov@postgrespro.ru>, Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, Andres Freund <andres@anarazel.de>, Michael Paquier <michael.paquier@gmail.com>, Oleg Bartunov <obartunov@gmail.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, David Steele <david@pgmasters.net>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2019-05-29T16:17:09Z
Lists: pgsql-hackers 
st 29. 5. 2019 v 17:49 odesílatel Dmitry Dolgov <9erthalion6@gmail.com>
napsal:

> Rebase after pg_indent. Besides, off the list there was a suggestion that
> this
> could be useful to accept more than one data type as a key for
> subscripting.
> E.g. for jsonb it probably makes sense to understand both a simple key
> name and
> jsonpath:
>
>     jsonb['a'] and jsonb['$.a']
>
> While to implement it can be technically relatively straightforward I
> guess, I
> wonder if there is any opinion about how valuable it could be and what it
> should looks like from the syntax point of view (since I believe a user
> needs
> to specify which type needs to be used).
>

It is difficult decision - possibility to use jsonpath looks great, but
necessity to cast every time is not friendly.

Probably there can be preferred type if subscripting is of unknown type.
There can be similar rules to function's parameters.

so jsonb['a'] -- key
    jsonb['$.a'] -- key
    jsonb['$.a'::jsonpath'] -- json path

but it can be source of bad issues - so I think we don't need this feature
in this moment. This feature can be implemented later, I think.

Regards

Pavel

Commits

  1. Throw error when assigning jsonb scalar instead of a composite object

  2. Filling array gaps during jsonb subscripting

  3. Implementation of subscripting for jsonb

  4. Allow ALTER TYPE to update an existing type's typsubscript value.

  5. Allow subscripting of hstore values.

  6. Support subscripting of arbitrary types, not only arrays.

  7. jit: Reference function pointer types via llvmjit_types.c.

  8. Teach contain_leaked_vars that assignment SubscriptingRefs are leaky.

  9. jit: Correct parameter type for generated expression evaluation functions.

  10. Renaming for new subscripting mechanism

  11. Fix assertion failure for SSL connections.

  12. Teach eval_const_expressions() to handle some more cases.