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I have two tables in PostGIS, each with two features(rows) and a rectangular geometry (polygon).

I would like to obtain the Symmetrical Difference from those two layers so that the result would be:

the resulting table has the attributes from the first table (df1), or the second (df2)

However when I try to use ST_SymDifference in PostGIS I get a different result:

CREATE TABLE test.symdifference_v04 AS
SELECT 
 test.df1.df1,
 test.df2.df2,
 ST_SymDifference(test.df1.geom,test.df2.geom)
FROM test.df1, test.df2

It seems that the ST_SymDifference is applied on a polygon to polygon basis i.e. df1 row 1 vs df2 row 1

df1 row 1 vs df2 row 2

df1 row 2 vs df2 row 1

df1 row 2 vs df2 row 2

with Multipolygons as a result.

How would I obtain the first mentioned result with the 6 polygons (fancy colors) instead of the 4 multiploygons in PostGIS?

This query should help you solve the problem:

variant 1 -

1) Combine two tables into one

DROP TABLE table3;
CREATE TABLE table3 as
SELECT table1.geom FROM table1
UNION ALL
SELECT table2.geom FROM table2

2) Remove unwanted parts:

CREATE TABLE table4 as
SELECT (ST_Dump(ST_SymDifference(a.geom, b.geom))).geom
FROM table3 a, 
 table1 b
WHERE ST_Overlaps(a.geom, b.geom)
UNION ALL
SELECT (ST_Dump(ST_SymDifference(a.geom, b.geom))).geom
FROM table3 a,
 table2 b
WHERE ST_Overlaps(a.geom, b.geom)

3) Cross the table itself:

CREATE TABLE table5 AS
SELECT (ST_Dump(ST_Difference(a.geom, b.geom))).geom
FROM table4 a,
table4 b
WHERE ST_Overlaps(a.geom, b.geom) OR ST_Intersects(a.geom, b.geom)


4) to remove the same geometry;

5) Remove the central small squares, and L - shaped parts

6) figure of the 11 items, 6 your, 5 not your...

Interesting geometric puzzle: -) ...