1

I have the split shapefiles like same size tiles. I want to show these merged on QGIS.

So, I tried to use Virtual Layer like following image. enter image description here

And, I wrote following SQL:

select * from north
UNION
select * from central
UNION
select * from west

But, the boundary line of shapefile shown. I want this,

enter image description here

In this case, how do I write SQL?

3

you have to UNION the geometry with ST_UNION and grouping the geometrys by one or more unique fields. The statement should be like this one (where name is the unique field/identifier in the example below):

SELECT ST_UNION(geometry), name FROM 
(
SELECT central.geometry, name FROM central 
UNION SELECT north.geometry, name FROM north 
UNION SELECT west.geometry, name FROM west
) 
GROUP BY name
0

1) If the structure of your input data is the same, you were very close:

select * from "north" UNION ALL select * from "central" UNION ALL select * from "west"

2) Now you need to connect sub-polygons that only touch the cut lines with an operator where with explicit identifiers, for example:

update union_table set geometry=ST_UNION(geometry) where union_table.ID =1 or union_table.ID =2...

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