inheritance and table

i don't have understand how works inheritance of tables...
if table B inherits from table A
- A and B must share primary keys?

No, currently there is no unique constraint that will force uniqueness across parent/child/sibling
tables. Just think of them as being nothing more than seperate table that share simlar
data-definitions.

When you select * from parent; you are essentially preforming a:

select * from parent
union
select * from childa
union
select * from childb ....;

if you want to only see the records in A then select * from only parent;

- if i isert record in B the record is replaced in A ?

can i avoid this?

This will not happen, you will end up with two records one A and one in B.

i would like to have this scenario:

table A

table B inheridts from A
table C inheridts from A

if i insert a record in B it must be insered only in B!
if i insert a record in C it must be insered only in C!

This is how is it will work.

http://www.postgresql.org/docs/8.1/interactive/ddl-inherit.html
Notice 5.8.1. Caveats

Regards,

Richard Broersma Jr.

nik600 wrote:

hi

i don't have understand how works inheritance of tables...

if table B inherits from table A

- A and B must share primary keys?

- if i isert record in B the record is replaced in A ?

can i avoid this?

i would like to have this scenario:

table A

table B inheridts from A
table C inheridts from A

if i insert a record in B it must be insered only in B!
if i insert a record in C it must be insered only in C!

is it possible?

thanks

Do you mean like this? (Notice the use of LIKE instead of INHERITS):

CREATE TABLE table_1 (
a int,
b int
)

CREATE TABLE table_2 (
LIKE table_1
)

(**Note: CREATE TABLE with INHERITS uses different syntax!**)

INSERT INTO table_1 (a, b) VALUES (1, 2);
INSERT INTO table_2 (a, b,) VALUES (3, 4);

Now,

SELECT * FROM table_1;

yeilds,

_a | b_
1 | 2

and not,

_a | b
_1 | 2
3 | 4

as it would've if you'd used INHERITS instead of LIKE.

--
erik jones <erik@myemma.com>
software development
emma(r)

Inheritance in postgre means you will have same fields definition
like the inherited table plus its own fields. So if table B is inherit
table A,
table B will have same field definition like A plus table B own
unique field(s).

It wont share primary keys, table B just have primary key in the same
field(s) like A
and records in table A wont be replaced by record(s) inserted to table B
or vice versa.

table A and table B basically a different entity, they just have same
fields definition.

Hope that will help you

ok i have understand

many thanks to all!