1 to many relationships
От | Dennis Gearon |
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Тема | 1 to many relationships |
Дата | |
Msg-id | 3E58592D.51713CB1@cvc.net обсуждение исходный текст |
Ответы |
Re: 1 to many relationships
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Список | pgsql-general |
If I have a child table and a parent table like so: ---BEGIN TABLE DEFS--------------------------------------------- create table parents( PriKey serial ); add primary constraint to PriKey; create table child( parent INT4 NOT NULL ); add foreign key constraint parent refs parent.PriKey ON DELETE CASCADE; ---BEGIN RELATIONSHIP DEF---------------------------------------- They are supposed to have the following relationship: parent(1T1)<------->(1TM)children textually explained as 'One parent has many children and must have at least one in order to exist, while a child must have one and only one parent in order to exist') ---BEGIN PROBLEM DEF / QUESTION --------=------------------------ For the 1T1 side of the relationship: the table defs will automatically cause the children to be caught or killed in the event that their parents disappear, no prob. For the 1TM side of the relationship: I don't see anything in the docs that says the PARENT will be sacrificed if their children don't survive or disappear, and I don't even know if there exists in any database the table definition option to enforce this. How is this done on different DB's? On Postgres? ---BEGIN GUESS--------------------------------------------------- Triggers? -- Carpe Dancem ;-) ----------------------------------------------------------------- Remember your friends while they are alive ----------------------------------------------------------------- Sincerely, Dennis Gearon
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