lindo query trayendo json

SELECT
    DISTINCT(exg.nombre_grupo_examination)
    , (SELECT
            array_to_json(array_agg(row_to_json(d)))::jsonb
        FROM (
            SELECT
                ex.nombre_item_examination
            FROM
                public.examination_item ex
            WHERE ex.codigo_grupo_examination = exg.codigo_grupo_examination
        ) d ) items
FROM
    public.examination_item exi
LEFT JOIN public.examination_grupo exg ON exg.codigo_grupo_examination = exi.codigo_grupo_examination
--******---
SELECT
    array_to_json(array_agg(row_to_json(subq)))::text json_data
FROM (
    SELECT
        DISTINCT(exg.nombre_grupo_examination)
        , (SELECT
                array_to_json(array_agg(row_to_json(d)))::jsonb
            FROM (
                SELECT
                    ex.codigo_grupo_examination
                    , ex.codigo_item_examination
                    , ex.nombre_item_examination
                    , CASE WHEN (TRIM(ex.unit_examination) = '') THEN null
                    WHEN (TRIM(ex.unit_examination) IS NULL) THEN null
                    ELSE CONCAT('[', ex.unit_examination, ']') END unit_examination
                FROM
                    public.examination_item ex
                WHERE ex.codigo_grupo_examination = exg.codigo_grupo_examination
            ) d ) items
    FROM
        public.examination_item exi
    LEFT JOIN public.examination_grupo exg ON exg.codigo_grupo_examination = exi.codigo_grupo_examination
) subq