[postgis-users] basic functionalities of PostGIS

[Ben Madin]

Apostolis,

On 04/01/2011, at 4:55 AM, ΑΠΟΣΤΟΛΟΣ ΛΕΛΕΝΤΖΗΣ wrote:

> Indeed, i understand the power of spatial SQL, but now i am a beginner, and i need a lot of work.
> 
> As i mentioned, i want to union two layers, typing a spatial SQL query.
> I want to take the same result, if i use the tool union of ArcGIS. But, i don't like to talk with terminal of ArcGIS, so i want to execute one of the classic spatial action, namely UNION (A or B).
> Because, i can't type the right command..could you help me???

It is fairly well documented, but this example unions two polygons (A Red, B Green).


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SELECT ST_AsText( 
	ST_Union( 
		ST_GeomFromText( 
			'POLYGON (( 1 1,1 3, 3 3 ,3 1,1 1))' -- Polygon A
		), 
		ST_GeomFromText( 
			'POLYGON((2 2, 2 4, 4 4, 4 2, 2 2))' -- Polygon B
		) 
	) 
);

                   st_astext                    
------------------------------------------------
 POLYGON((1 1,1 3,2 3,2 4,4 4,4 2,3 2,3 1,1 1))
(1 row)