Techniques for selecting an object's attribute

User_1871

I have a column that is an object datatype — SDO_GEOMETRY:

create table my_tbl (shape sdo_geometry);
insert into my_tbl (shape) values (sdo_geometry('LINESTRING(1 2,3 4)'));

The object has attributes (2.2 SDO_GEOMETRY Object Type):

SDO_GTYPE
SDO_SRID
SDO_POINT
SDO_ELEM_INFO
SDO_ORDINATES

I want to select an attribute from the object. I can do that by using a table alias:

select
  a.shape.sdo_gtype
from
  my_tbl a

Out of curiosity, are there any other ways to select object attributes, other than creating an alias?

As a non-expert, it seems strange to me that the alias is necessary. Of course, creating an alias isn't a big deal, but I would have guessed that I could just use the dot notation without an alias: select shape.sdo_gtype from my_tbl. But that doesn't work: ORA-00904: "SHAPE"."SDO_GTYPE": invalid identifier .

BluShadow

https://community.oracle.com/tech/developers/discussion/4498503/techniques-for-selecting-an-objects-attribute

It's to do with how the parser tries to see database objects, so shape.sdo_gtype assumes that the "shape" is a table alias and not the object name. Sure, you can use the methods you've already mentioned e.g. alias the table and prefix with that, or use TREAT. You can also surround the object name in braces/brackets to indicate it's not a table alias...

SQL> select (shape).sdo_gtype
  2  from   my_tbl
  3  /

(SHAPE).SDO_GTYPE
-----------------
             2002

User_1871

It looks like I can use the TREAT() function:

select
  treat(shape as sdo_geometry).sdo_gtype
from
  my_tbl

https://dbfiddle.uk/?rdbms=oracle_21&fiddle=9869d0a53afd0bef3d256540970aec72

Although that's not much different than the alias option.

Related:

Get ST_GEOMETRY object's attribute

User_H3J7U

References to Object Type Attributes and Methods

BluShadow

https://community.oracle.com/tech/developers/discussion/4498503/techniques-for-selecting-an-objects-attribute

It's to do with how the parser tries to see database objects, so shape.sdo_gtype assumes that the "shape" is a table alias and not the object name. Sure, you can use the methods you've already mentioned e.g. alias the table and prefix with that, or use TREAT. You can also surround the object name in braces/brackets to indicate it's not a table alias...

SQL> select (shape).sdo_gtype
  2  from   my_tbl
  3  /

(SHAPE).SDO_GTYPE
-----------------
             2002