Why UPDATE gl SET gl.glnum = gl.glnum; cause error when UPDATE gl SET glnum = glnum; is OK ?

Hi all,

I was juste wondering why the following code don't work:
 UPDATE gl SET gl.glnum = gl.glnum
ERROR:  column "gl" of relation "gl" does not exist

While the following works:
UPDATE gl SET glnum = glnum;

Query returned successfully: 177 rows affected, 281 ms execution time.

the TABLE.COLUMN is not in the SQL standard ?

Thanks
/David