"=" or ":=" ?

[BERTRAND Joël <joel.bertrand@xxxxxxxxxxx>]

	Hello,

	I'm trying to optimize assign_vertex_id() function provided by 
pgRouting/PostGIS. In this function, I can see :

DECLARE
      points record;
      i record;
      source_id int;
      target_id int;
      pre varchar;
      post varchar;

      srid integer;
                    			
      BEGIN
                    			
	    BEGIN
	        DROP TABLE vertices_tmp;
        	EXCEPTION
			WHEN UNDEFINED_TABLE THEN
                END;
                    						
		EXECUTE 'CREATE TABLE vertices_tmp (id serial)';	
                							
		FOR i IN EXECUTE 'SELECT srid FROM geometry_columns WHERE 
f_table_name='''|| quote_ident(geom_table)||'''' LOOP
		END LOOP;
		
		srid := i.srid;
		
		EXECUTE 'SELECT addGeometryColumn(''vertices_tmp'', ''the_geom'', 
'||srid||', ''POINT'', 2)';
                    							 

                CREATE INDEX vertices_tmp_idx ON vertices_tmp USING 
GIST (the_geom);
		
                pre = '';
                post = '';

	I don't understand last assignations. In pgsql documentation, ther is 
written that all assignations have to be written with ":=", not with 
"=". What is the difference between "=" and ":=" ? I don't find any 
information about "=".

	Regards,

	JKB

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