SELECT * FROM
(
(SELECT the_geom, cell_id, cdi_2018_07_01 as v, DATE '2018-07-01' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_04_01 as v, DATE '2018-04-01'  AS d  FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_04_11 as v, DATE '2018-04-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_04_21 as v, DATE '2018-04-21' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_05_01 as v, DATE '2018-05-01' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_05_11 as v, DATE '2018-05-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_05_21 as v, DATE '2018-05-21' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_06_01 as v, DATE '2018-06-01' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_06_11 as v, DATE '2018-06-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_06_21 as v, DATE '2018-06-21' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_07_11 as v, DATE '2018-07-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_07_21 as v, DATE '2018-07-21' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_08_01 as v, DATE '2018-08-01' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_08_11 as v, DATE '2018-08-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_08_21 as v, DATE '2018-08-21' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_09_01 as v, DATE '2018-09-01' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_09_11 as v, DATE '2018-09-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_09_21 as v, DATE '2018-09-21' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_10_01 as v, DATE '2018-10-01' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_10_11 as v, DATE '2018-10-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_10_21 as v, DATE '2018-10-21' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_11_01 as v, DATE '2018-11-01' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_11_11 as v, DATE '2018-11-11' AS d FROM cdi_cr_2018_04_2018_11) union
(SELECT the_geom, cell_id, cdi_2018_11_21 as v, DATE '2018-11-21' AS d FROM cdi_cr_2018_04_2018_11)
) as abc
where v is not NULL