Re: update without SET ?

Lost me here David. I can't seem to bridge the gap between your pseudo-code
and an actual example.

setup:
CREATE TABLE mytest
(key bigint NOT NULL,
header bigint NOT NULL,
ident bigint NOT NULL,
static01 character varying(100),
static02 character varying(220) );

INSERT into mytest
SELECT * FROM
json_populate_record(null::mytest,'{"key":22,"header":44,"ident":66,"static01":"this","static02":"that"}');

And here is my failed interpretation of your example: *(I used inline JSON
string just for ease. In real life it will be a variable of type JSON.)*

UPDATE mytest
SET header = (CASE WHEN src.header = 'header' THEN src.header ELSE
mytest.header END)
FROM (
SELECT * FROM json_populate_record(null::mytest,
'{"key":22,"header":44,"ident":null,"static02":"that"}')
CROSS JOIN
(SELECT '{"key":22,"header":44,"ident":null,"static02":"that"}') AS
source_json
) src
WHERE mytest.key = src.key;

On Wed, Feb 3, 2016 at 2:20 PM, David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> On Wed, Feb 3, 2016 at 2:51 PM, David G. Johnston <
> david(dot)g(dot)johnston(at)gmail(dot)com> wrote:
>
>> On Wed, Feb 3, 2016 at 11:49 AM, Michael Moore <michaeljmoore(at)gmail(dot)com>
>> wrote:
>>
>>> I want to UPDATE a table but I will not know until run time which
>>> columns will be updated. I would like to do something like this:
>>> update mytest t (SELECT * FROM
>>> json_populate_record(null::mytest,'{"key":22,"header":44,"ident":66,"static01":"this","static02":"that"}'));
>>>
>>> In other words, I will be receiving a json document on an input
>>> parameter. The columns named in the json document can be a sub set of those
>>> that exist in the table.
>>>
>>>
>> If a key is defined but has a value of null what do you want to do?
>>
>> ​not fully tested...​
>>
>> UPDATE mytest
>> SET col1 = COALESCE(src.col1, mytest.col1)
>> ​FROM (SELECT * FROM json_populate_record(...)) src;​
>>
>> json_populate_record outputs the full structure of mytest regardless of
>> its input so simply match every column and use COALESCE to choose between
>> the value in the json and the value already on the table.
>>
>> Aside from the null json value issue that should work - if not you
>> probably need to describe your problem in more detail.
>>
>>
> ​Modification thought to deal with JSON null values on existing keys​:
>
> UPDATE mytest
> SET col1 = (CASE WHEN src.json_value ? 'col1' THEN src.col1 ELSE
> mytest.col1 END)
> FROM (
> SELECT *
> FROM json_populate_record(json_value)
> CROSS JOIN
> SELECT json_value AS source_json
> ) src WHERE mytest.key = src.key;
>
> ​David J.​
>
>