Postgres: expand JSON array elements into values with their index?

Question

I have a table with a column containing a JSON array. As an example:

with example as (
    select '["a", "b"]'::jsonb as col
    union select ('["c", "d", "e"]'::jsonb) as col
)
select col from example

Returns:

col
["a", "b"]
["c", "d", "e"]

I can use jsonb_array_elements to expand out each array into rows:

select jsonb_array_elements(col) from example

Returns:

jsonb_array_elements
"a"
"b"
"c"
"d"
"e"

I want the index of each array element along with the element itself (a bit like Python's enumerate), like so:

jsonb_array_elements    array_index
"a"                     1
"b"                     2
"c"                     1
"d"                     2
"e"                     3

How can I do this?

My application has read-only access, so I cannot create functions.

Answer 1

Use with ordinality:

with example (col) as (
  values 
    ('["a", "b"]'::jsonb),  
    ('["c", "d", "e"]'::jsonb)
)
select t.*
from example, jsonb_array_elements(col) with ordinality as t(e,idx)

returns:

e   | idx
----+----
"a" |   1
"b" |   2
"c" |   1
"d" |   2
"e" |   3

with ordinality can only be used if you use the set returning function in the from clause, which is highly recommended anyway.