Extractvalue, extract, xmlsequence

Question

Could someone explain what extractvalue, xmlsequence and extract is doing in the following query:
select
   extractvalue(value(a),'Notebook/@Brand') As Brand
  ,extractvalue(value(a),'Notebook/@Model') As Model
from prod_xml_tab b,
table( xmlsequence( extract( demo_field,'Product/Notebook' ) ) ) a
where demo_field is not null;I went through documentation and still don't get it, and need some basic explanation step by step. for example, what is actually EXTRACT returning for first and second row?
the code for table and data is as follows:
create table prod_xml_tab (demo_field xmltype);
insert into prod_xml_tab values('
  <Product type="Laptop">
              <Notebook Brand="HP" Model="Pavilion dv6-3132TX Notebook">
                          <Harddisk>640 GB</Harddisk>
                          <Processor>Intel Core i7</Processor>
                          <RAM>4 GB</RAM>
                          <Price>1189</Price>
                          <Display Type="LED" MonitorSize="15.6"/>
                          <Weight>4.14</Weight>
              </Notebook>
              <Notebook Brand="HP" Model="HP Pavilion dv6-3032TX Notebook">
                          <Harddisk>640 GB</Harddisk>
                          <Processor>Intel Core i7</Processor>
                          <RAM>6 GB</RAM>
                          <Price>1104</Price>
                          <Display Type="LED" MonitorSize="15.6"/>
                          <Weight>4.1</Weight>
              </Notebook>
              <Notebook Brand="HP" Model="Pavilion dv6-3079TX Notebook">
                          <Harddisk>500 GB</Harddisk>
                          <Processor>Intel Core i7</Processor>
                          <RAM>4 GB</RAM>
                          <Price>1099</Price>
                          <Display Type="LED" MonitorSize="15.6"/>
                          <Weight>4.14</Weight>
              </Notebook>
</Product>');
insert into prod_xml_tab values('
<Product>
              <Notebook Brand="Toshiba" Model="Satellite A660/07R 3D Notebook">
                          <Harddisk>640 GB</Harddisk>
                          <Processor>Intel Core i7</Processor>
                          <RAM>4 GB</RAM>
                          <Price>1444</Price>
                          <Display Type="LED" MonitorSize="15.6"/>
                          <Weight>4.88</Weight>
              </Notebook>
</Product>');

Answer 1

943276 wrote:
thank you... this is a bit confusing when trying to reproduce excellent example on wrong version.
anyway, do you know what is this (+) doing formally? is this a notation similar to left outer join? I noticed it in some other example which I cannot find now.It is an outer join.
Example:
SQL> ed
Wrote file afiedt.buf
  1  WITH xml_table AS
  2      (SELECT xmltype('
  3      <root>
  4        <child name="name1">
  5          <grandchild name="name11">
  6            <greatgrandchild name="name111"/>
  7            <greatgrandchild name="name112"/>
  8          </grandchild>
  9          <grandchild name="name12"/>
10       </child>
11       <child name="name2">
12         <grandchild name="name21">
13            <greatgrandchild name="name211"/>
14         </grandchild>
15         <grandchild name="name22"/>
16       </child>
17     </root>') object_value FROM dual)
18  select po.child_name, gc.gchild_name, ggc.ggchild_name
19  from   xml_table p
20        ,xmltable('/root/child'
21                  passing p.object_value
22                  columns child_name  varchar2(100) path '@name'
23                         ,gchild      xmltype       path 'grandchild'
24                 ) po
25        ,xmltable('/grandchild'
26                  passing po.gchild
27                  columns gchild_name varchar2(100) path '@name'
28                         ,ggchild     xmltype       path 'greatgrandchild'
29                 ) (+) gc
30        ,xmltable('/greatgrandchild'
31                  passing gc.ggchild
32                  columns ggchild_name varchar2(100) path '@name'
33*               ) (+) ggc
SQL> /
CHILD_NAME GCHILD_NAME GGCHILD_NAME
name1      name11      name111
name1      name11      name112
name1      name12
name2      name21      name211
name2      name22without the outer joins it would just give...
SQL> ed
Wrote file afiedt.buf
  1  WITH xml_table AS
  2      (SELECT xmltype('
  3      <root>
  4        <child name="name1">
  5          <grandchild name="name11">
  6            <greatgrandchild name="name111"/>
  7            <greatgrandchild name="name112"/>
  8          </grandchild>
  9          <grandchild name="name12"/>
10       </child>
11       <child name="name2">
12         <grandchild name="name21">
13            <greatgrandchild name="name211"/>
14         </grandchild>
15         <grandchild name="name22"/>
16       </child>
17     </root>') object_value FROM dual)
18  select po.child_name, gc.gchild_name, ggc.ggchild_name
19  from   xml_table p
20        ,xmltable('/root/child'
21                  passing p.object_value
22                  columns child_name  varchar2(100) path '@name'
23                         ,gchild      xmltype       path 'grandchild'
24                 ) po
25        ,xmltable('/grandchild'
26                  passing po.gchild
27                  columns gchild_name varchar2(100) path '@name'
28                         ,ggchild     xmltype       path 'greatgrandchild'
29                 ) gc
30        ,xmltable('/greatgrandchild'
31                  passing gc.ggchild
32                  columns ggchild_name varchar2(100) path '@name'
33*               ) ggc
SQL> /
CHILD_NAME GCHILD_NAME GGCHILD_NAME
name1      name11      name111
name1      name11      name112
name2      name21      name211