trigger function postgres

WITH regular_grid_median AS (
    SELECT
      ST_median(ref_norm_int_345_355) AS median_val,
      ST_AsKML(first(rgp_view.grid_pixel)) AS polygon
    FROM
      (SELECT * FROM regular_grid_pixel rgp
                JOIN regular_grid_pixel_vertex_intersection rgp_vi ON rgp_vi.id_poly=rgp.pid
                JOIN regular_grid rg ON rgp.rgid=rg.rgid
                WHERE view_short_name='bluetongue_area_0.6dpp_0.84dpp')
      rgp_view INNER JOIN meas_data_small ms ON rgp_view.id_meas=ms.data_ind
    GROUP BY rgp_view.id_poly
)
SELECT
'<Style><PolyStyle><color>50' ||
(SELECT '50'||to_hex(r)||to_hex(g)||to_hex(b) FROM color_palette WHERE name='BuYlRd' AND index=(((median_val-minmax.min)*norm_factor)::INT)) ||
'</color></PolyStyle></Style>' ||
 polygon
FROM regular_grid_median , (SELECT min(median_val) as min,max(median_val) as max,254.0/(max(median_val) - min(median_val)) as norm_factor FROM regular_grid_median) minmax;