I'm trying to get the following scenario to work:
I have three tables, and one of them (IncidentDetail) is to hold incident information of the other two (Incident and PendIncident). I want the IncidentDetail table to reference either an incident in the Incident, or PendIncident table so it could exist in either place. How would I set up the constraints?
Table 1 - Incident:
+--------------------+
| IncidentNbr | Desc |
+--------------------+
Table 2 - PendIncident:
+------------------------+
| PendIncidentNbr | Desc |
+------------------------+
Table 3 - IncidentDetail:
+-----------------------+
| IncidentNbr | Details |
+-----------------------+
The IncidentDetail table will have a FK constraint so that the IncidentDetail.IncidentNbr will need to have a value in either the Incident.IncidentNbr column OR the PendIncident.PendIncidentNbr column.
Is it possible to have a FK constraint on a single column that references into two different tables or will I need a second PendIncidentNbr column in the IncidentDetail table that has its own FK constraint to PendIncident.PendIncidentNbr?
Is that enough to ensure that the IncidentDetail table satisfies at least one of the FK constraints?
The other approach I can think of is to drop the FK constraints all together and use a check constraint where either the IncidentDetail.IncidentNbr column or IncidentDetail.PendIncidentNbr column has a value.
You can have FK constraints on a single column that references into two different tables but it will not work with your use case.
Since an incidentNbr exists either in Incident table or PendIncident table at any given point in time, having two FK constraints in IncidentDetail table will fail as soon as you attempt to insert a record in this child table. Since the incident exists in one parent table but not the other, it will throw an integrity constraint violation error w.r.t. second FK.
Using a check constraint can be a viable solution for this scenario.
Code snippet for quick reference -
Create table table_a(col_a number primary key);
Create table table_b(col_b number primary key);
Create table table_c(col_c number);
ALTER TABLE table_c
ADD CONSTRAINT fk_c_a
FOREIGN KEY (col_c)
REFERENCES table_a(col_a);
ALTER TABLE table_c
ADD CONSTRAINT fk_c_b
FOREIGN KEY (col_c)
REFERENCES table_b(col_b);
Insert into table_a values(100);
Insert into table_b values(200);
Insert into table_c values(100); —-This statement will throw integrity constraint violation error
No, a foreign key can only refer to one parent table.
You will either need two separate columns in INCIDENT_DETAIL, each with its own FK, or else combine INCIDENT and PENDINCIDENT into a single table with a type or status column.
The fact that you find yourself with a single column that seems to refer to either of two parent tables suggests to me that perhaps they are really the same thing at different states of processing.
I want to define a foreign key constraint between the table Speler and the table Wedstrijd. I want the key on the Wedstrijd table, but when I use this code in my SQL console:
ALTER TABLE Speler
ADD FOREIGN KEY (idSpeler) REFERENCES Wedstrijd(idWedstrijd);
It puts a key on the table Speler and on the table Wedstrijd
Thanks for your time!
ALTER TABLE Wedstrijd
ADD FOREIGN KEY (idWedstrijd) REFERENCES Speler(idSpeler);
Instead of "solving" what you perceive as your problem, I think you have a different problem:
By mapping idSpeler to idWedstrijd, you are basically saying that a Speler (Player) is equal to a Wedstrijd (Match). That becomes a 1:1 relation which is then shown as a line with two yellow 'key'-endings (assuming you are using SQL Server).
It is very likely to me that instead you need to create a linking table WedstrijdSpeler that sits between the other two tables.
Then the new table WedstrijdSpeler needs to be given 2 Foreign Keys:
WedstrijdSpeler.idWedstrijd -> Wedstrijd.idWedstrijd
WedstrijdSpeler.idSpeler -> Speler.idSpeler.
Then you can give WedstrijdSpeler either a combined Primary Key (containing both fields idWedstrijd and idSpeler), or you can add a third field idWedstrijdSpeler and make that the Primary Key. Either approach will do, it is up to you.
I have a table and I need to insert a huge number of records, so I create my table without primary key to make the insert faster. when I finished insert, I create primary key for that table using this command:
ALTER TABLE MyTable ADD CONSTRAINT PK_MyTable PRIMARY KEY (MyTableId)
The problem is if I delete the table inside SQL Server management studio then the next time when I want to create this primary key, it says :
The CREATE UNIQUE INDEX statement terminated because
a duplicate key was found for the object name
I need to let SQL knows that this primary key is connected to that table and must automatically be deleted when the table is being deleted.
I guess this is not a primary key problem. It is a problem with your data. You are not allowed to create a primary key because you have a duplicate value in your primary key column.
You could run a query to confirm that you have a duplicate.
SELECT
MyTableId,
COUNT(*)
FROM
MyTable
GROUP BY
MyTableId
HAVING
COUNT(*) > 1
The Best Answer to dropping the table containing Primary and foreign constraints is :
Step 1 : Drop the Primary key of the table.
Step 2 : Now it will prompt whether to delete all the foreign references or not.
Step 3 : Delete the table.
I'm having a problem referencing a Foreign Key from another table that has already been created with data imported.
ALTER TABLE CSEA_BOOK
ADD CONSTRAINT FK_BOOK_CASE_ID FOREIGN KEY (CASE_ID)
REFERENCES CSEA_CASE(CASE_ID);
I can create it just fine but when you
SELECT *
FROM CSEA_CASE a, CSEA_BOOK b
WHERE a.CASE_ID = b.CASE_ID;
everything comes back NULL where I know it should contain data.
Am I doing something out of order or Sequence?
I need to make some changes to a SQL Server 2008 database.
This requires the creation of a new table, and inserting a foreign key in the new table that references the Primary key of an already existing table. So I want to set up a relationship between my new tblTwo, which references the primary key of tblOne.
However when I tried to do this (through SQL Server Management Studio) I got the following error:
The columns in table 'tblOne' do not
match an existing primary key or
UNIQUE constraint
I'm not really sure what this means, and I was wondering if there was any way around it?
It means that the primary key in tblOne hasn't been properly declared - you need to go to tblOne and add the PRIMARY KEY constraint back onto it.
If you're sure that tblOne does have a PRIMARY KEY constraint, then maybe there are multiple tblOne tables in your DB, belonging to different schemas, and your references clause in your FK constraint is picking the wrong one.
If there's a composite key (which your comment would indicate), then you have to include both columns in your foreign key reference also. Note that a table can't have multiple primary keys - but if it has a composite key, you'll see a key symbol next to each column that is part of the primary key.
If you have a composite key the order is important when creating a FK, and sometimes the order is not how it is displayed.
What I do is go to the Keys section of the table1 and select script primary key as create to clipboard and then create FK using the order as shown in script
I've had this situation that led me to this topic. Same error but another cause. Maybe it will help someone.
Table1
ColA (PK)
ColB (PK)
ColC
Table2
ID (PK)
ColA
COLB
When trying to create foreign key in Table2 I've choose values from combobox in reverse order
Table1.ColB = Table2.ColB
Table1.ColA = Table2.ColA
This was throwing me an error like in topic name. Creating FK keeping order of columns in Primary key table as they are, made error disappear.
Stupid, but.. :)
If you still get that error after you have followed all advice from the above answers and everything looks right.
One way to fix it is by Removing your Primary keys for both tables, Save, Refresh, and add them again.
Then try to add your relationship again.
This Error happened with me When I tried to add foreign key constraint starting from PrimaryKey Table
Simpy go to other table and and create this foreign key constraint from there (foreign key Table)
This issue caught me out, I was adding the relationship on the wrong table. So if you're trying to add a relationship in table A to table B, try adding the relationship in table B to table A.
That looks like you are trying to create a foreign key in tblTwo that does not match (or participate) with any primary key or unique index in tblOne.
Check this link on MSDN regarding it. Here you have another link with a practical case.
EDIT:
Answwering to your comment, I understand you mean there are 2 fields in the primary key (which makes it a composite). In SQL it is not possible to have 2 primary keys on the same table.
IMHO, a foreign key field should always refer to a single register in the referenced table (i.e. the whole primary key in your case). That means you need to put both fields of the tblOne primary key in tblTwo before creating the foreign key.
Anyway, I have investigated a bit over the Internet and it seems SQL Server 2008 (as some prior versions and other RDBMS) gives you the possibility to reference only part of the primary key as long as this part is a candidate key (Not Null and Unique) and you create an unique constraint on it.
I am not sure you can use that in your case, but check this link for more information on it.
I have found that the column names must match.
Example:
So if tblOne has id called categoryId a reference in tblTwo must also be called categoryId.
_tblname, primary key name, foreign key_
tblOne, "categoryId", none
tblTwo, "exampleId", "categoryId"
I noticed this when trying to create foreign key between 2 tables that both had the column name "id" as primary key.
If nothing helps, then this could be the reason:
Considering this case:
Table A:
Column 1 (Primary Key)
Column 2 (Primary Key)
Column 3
Column 4
Table B:
Column a (Primary Key)
Column b
Column c
when you are defining a dependency B to A, then you are forced to respect the order in which the primaries are defined.
That's mean your dependency should look like this:
Table A Table B
Column 1 Column b
Column 2 Column c
AND NOT:
Table A Table B
Column 2 Column c
Column 1 Column b
then this will lead to the error you are encountering.
I've found another way to get this error. This can also happen if you are trying to make a recursive foreign key (a foreign key to the primary key in the same table) in design view in SQL Management Studio. If you haven't yet saved the table with the primary key it will return this message. Simply save the table then it will allow you to create the foreign key.
If you have data in your tables this could be the issue.
In my case I had some data in the Account table that I loaded at 3 pm, and some data in Contact table that I loaded at 3:10 pm, so Contact table had some values that weren't in my Account table yet.
I ended up deleting these values from the contact table and then managed to add a key without any problems.
Kindly also see that there are no existing data inside the table where the primary key is defined while setting the foreign key with another table column.
this was the cause of the error in my case.
I had to take backup empty the table set the relationship and then upload the data back.
sharing my experience
Was using ms sql smss