On 06/23/2014 11:06 AM, Robert Haas wrote:
On Fri, Jun 20, 2014 at 11:26 AM, Joey Caughey
<jcaug...@parrotmarketing.com> wrote:
I’m having an issue with JSON requests in Postgres and was wondering if
anyone had an answer.
I have an orders table with a field called “json_data”.
In the json data there is a plan’s array with an id value in them.
{ "plan”: { “id”: “1” } } }
I can do regular queries that will work, like so:
SELECT json_data->>’plan'->>’id' as plan_id FROM orders;
But if I try to query on the data that is returned it will fail:
SELECT json_data->>’plan'->>’id' as plan_id FROM orders WHERE plan_id = 1;
OR
SELECT json_data->>’plan'->>’id' as plan_id FROM orders GROUP BY plan_id;
OR
SELECT json_data->>’plan'->>’id' as plan_id FROM orders ORDER BY plan_id;
Is this something that has been overlooked? or is there another way to go
about this?
You might find a sub-SELECT helpful:
SELECT * FROM (SELECT json_data->>’plan'->>’id' as plan_id FROM
orders) x WHERE plan_id = 1
It might be a generally useful thing for WHERE-clause items to be able
to reference items from the target list by alias, or maybe it's
problematic for some reason that I don't know about, but right now
they can't.
Once again,
json_data->>’plan'->>’id'
is an expression guaranteed to fail, since ->> returns text but expects
its left hand o0perand to be json, unlike
json_data->’plan'->>’id'
or
json_data#>>'{plan,id}'
So I don't believe the OPs original statement about what is and isn't
working. The alias issue, of course, is not at all JSON-specific, and
the subselect is one solution - a CTE is another. But you CAN use the
alias in an ORDER BY or GROUP BY.
cheers
andrew
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