PostGIS 3 table join & classification with MapServer

Question

I have been trying to create a mapServer map by joining 3 table then create classes on those joins (2000 - red, 2010 - green, 2020 - blue)

I am not getting an error but noting is display

$query = "geom FROM (
   SELECT 
     a.geom, 
     b.geom, 
     c.geom 
   FROM 
     data2000 as a 
   INNER JOIN data2015 as b 
   ON b.province = '$variable' 
   INNER JOIN data2020 as c
   ON b.province = '$variable'
   ) AS subquery USING UNIQUE gid USING SRID=4326";

I would also like to see this represented in

CLASS
     data 1
     STYLE
        ....
     END
END
CLASS
     data 2
     STYLE
        ....
     END
END
CLASS
     data 3
     STYLE
        ....
     END
END

Answer 1

First use join query as in example below

DATA "target_point from (select 
    events_objects_tbl.target_point, 
    events_objects_tbl.source_point, 
    geo_units_tbl.geo_unit_group 
from events_objects_tbl 
JOIN geo_units_tbl 
ON geo_units_tbl.id = events_objects_tbl.target_geo_unit_id 
   AND geo_units_tbl.date = events_objects_tbl.date
) as subquery using unique oid using srid=4326"

then use class with expression

CLASS
  NAME "events_targets_a"
  GROUP "events_targets"
  EXPRESSION ("[geo_unit_group]" = "Группа А")
  STYLE
    SYMBOL "a_targets_cluster"
    SIZE 64
  END
END