[SOLVED] json_array_elements with null values

json_array_elements with null values

I'm using PostgreSQL 9.4.5, 64 bit on windows. I've got some irregular sized arrays. I want to use json_array_elements to expand the arrays similar to the following code

with outside as (select (json_array_elements('[[],[11],[21,22,23]]'::json)) aa, json_array_elements('[1,2,3]'::json)bb) 
select json_array_elements_text(aa), bb from outside

However, when i run this, i get

aa | bb
------- 
11 |  2
21 |  3
22 |  3
23 |  3

The empty array in column aa is dropped on the floor along with the the value of 1 in column bb

I would like to get

aa   | bb
---------- 
null |  1
11   |  2
21   |  3
22   |  3
23   |  3

Also, is this a bug in PostgreSQL?

Solution

You are using the right functions, but the wrong JOIN. If you (possibly) don't have rows on one side of the JOIN & you want to keep the rows from the other side of the JOIN & use NULLs to "pad" rows, you'll need an OUTER JOIN:

with outside as (
    select json_array_elements('[[],[11],[21,22,23]]') aa,
           json_array_elements('[1,2,3]') bb
) 
select    a, bb
from      outside
left join json_array_elements_text(aa) a on true

Note: it may seem strange to see on true as the joining condition, but it is actually quite general, when you are using LATERAL joins (which is implicit when you use a set returning function (SRF) directly in the FROM clause).

http://rextester.com/KNW13145

Edit: your original query does not involve a JOIN directly, but worse: you use a SRF in the SELECT clause. This is almost like a CROSS JOIN, but actually it has its own rules. Don't use that unless you know exactly what you are doing and why you need that.