Return elements of Redshift JSON array on separate rows

Thanks to this inspired blog post, I've been able to craft a solution. This is:

1. Create a look-up table to effectively 'iterate' over the elements of each array. The number of rows in this table has be equal to or greater than the maximum number of elements of arrays. Let's say this is 4 (it can be calculated using SELECT MAX(JSON_ARRAY_LENGTH(metadata)) FROM input_table):

   CREATE VIEW seq_0_to_3 AS    SELECT 0 AS i UNION ALL                                          SELECT 1 UNION ALL    SELECT 2 UNION ALL        SELECT 3          );

2. From this, we can create one row per JSON element:

   WITH exploded_array AS (                                                                              SELECT id, JSON_EXTRACT_ARRAY_ELEMENT_TEXT(metadata, seq.i) AS json    FROM input_table, seq_0_to_3 AS seq    WHERE seq.i < JSON_ARRAY_LENGTH(metadata)  )SELECT *FROM exploded_array;

   Producing:

    id | json------------------------------ 1  | {"pet":"dog"} 1  | {"country":"uk"} 2  | {"pet":"cat"} 4  | {"country":"germany"} 4  | {"education":"masters"} 4  | {"country":"belgium"}

3. However, I was needing to extract the field names/values. As I can't see any way to extract JSON field names using Redshift's limited functions, I'll do this using a regular expression:

   WITH exploded_array AS (                                                                                           SELECT id, JSON_EXTRACT_ARRAY_ELEMENT_TEXT(metadata, seq.i) AS json    FROM input_table, seq_0_to_3 AS seq    WHERE seq.i < JSON_ARRAY_LENGTH(metadata))SELECT id, field, JSON_EXTRACT_PATH_TEXT(json, field)FROM (    SELECT id, json, REGEXP_SUBSTR(json, '[^{"]\\w+[^"]') AS field    FROM exploded_array);

There is generic version for CREATE VIEW seq_0_to_3. Let's call it CREATE VIEW seq_0_to_n. This can be generated by

CREATE VIEW seq_0_to_n AS (      SELECT row_number() over (                          ORDER BY TRUE)::integer - 1 AS i    FROM <insert_large_enough_table> LIMIT <number_less_than_table_entries>);

This helps in generating large sequences as a view.