One-to-Many Restriction

Question

We have two tables with a one-to-many relationship. We would like to apply a restriction to at least one child record for this parent record.

Is it possible?

If not, will you replace the circuit with a more complex one to support this limitation? If so, how would you do it?

Edit: I am using SQL Server 2005

Answer 1

, " ". , , , , .

.

Answer 2

, back-end , PostgreSQL.

Answer 3

?

Create Table ParentTable
(
ParentID
ChildID not null,
Primary Key (ParentID), 
Foreign Key (ChildID ) references Childtable (ChildID));
)

- , , before insert trigger .

CREATE or REPLACE TRIGGER trigger_name
BEFORE INSERT
    ON ParentTable
    FOR EACH ROW 
BEGIN

    -- ( insert new row into ChildTable )
    -- update childID column in ParentTable 

END;

Answer 4

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- SQL Server.

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2) CTE , CTE , ( ). , , .

3) , , . . , , , .

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, . , null ( ). ( ), , .

, SQL Server , .

- , !

P.S. , , , , , , .

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Answer 5

, Oracle rel.11.2.4.

• , FK PK . - .
• , , :

, PK, COUNT PK. - , NO_DATA_FOUND 0.

CHILD_COUNT .

CHECK CHILD_COUNT CHILD_COUNT > 0

:

• ​​ . , , CHILD_COUNT > 0 CHECK .
• ​​ ​​ ; , COMMIT.
• ​​ , CHILD_COUNT COMMIT .
• , FOREIGN KEY . ( )
• , CHILD_COUNT .

NOTE. I do not need a virtual column if Oracle allowed to use CHECK constraintsbased on user-defined functions in rel.11.2.4.