Обсуждение: inheritance and table
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
> 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 > 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 > > ---------------------------(end of broadcast)--------------------------- > TIP 4: Have you searched our list archives? > > http://archives.postgresql.org >
ok i have understand many thanks to all! On 6/27/06, Erik Jones <erik@myemma.com> wrote: > 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) > >