Removed the last element from a json[]?

I have a json[] array (_result_group) in PostgreSQL 9.4, and I want to remove its last json element (_current). I prepared with:

_result_group := (SELECT array_append(_result_group,_current));

And tried to remove with:

SELECT _result_group[1:array_length(_result_group,1) -1] INTO _result_group;

But it didn’t work.
How to do this?

Answer

To remove the last element from any array (including json[]) with the means of Postgres 9.4, obviously within plpgsql code:

_result_group := _result_group[1:cardinality(_result_group)-1];

Assuming a 1-dimensional array with default subscripts starting with 1.

You get an empty array for empty array input and null for null.

According to the manual, cardinality() …

returns the total number of elements in the array, or 0 if the array is empty

Then just take the array slice from 1 to cardinality -1.

Then again, your attempt should work as well:

SELECT _result_group[1:array_length(_result_group,1) -1] INTO _result_group;

For non-standard array subscripts see:

• Normalize array subscripts for 1-dimensional array so they start with 1