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.
Related
I have 2 simple tables designed as shown below:
Users:
Categories:
Now I would like to set the username as foreign key on categories table so this is what I have done but getting the error as shown below:
Am I doing the right way? Or can anyone suggest me the right way of doing this ?
*NOTE: I have tried to remove the primary key from the 2 tables and added them back and tried but showing me the same error.
You are not doing it the right way - hence the error. Put userid in your categories table and join to users if you need the name.
In fact, if that field represents the person who created the category, it should be named something like CreatedByUserId. It should still reference users.userid.
Impose a unique constraint on the username column in Users table. Then you can create the FK as shown. That said, having username in both tables is not a very good design. You should remove username and include userid in Categories table and make that a FK instead.
A foreign key constraint does not have to be linked only to a primary
key constraint in another table; it can also be defined to reference
the columns of a UNIQUE constraint in another table.
in Create Foreign Key Relationships
You have to set a constraint in table Users in order to username to be unique.
Try to change in the table Categories the name of the foreign key field.
It seems that it "autowire" fields using their name. What i mean is : change Categories.username to Categories.userid.
Your column username in the table users must have a unique constraint if you want to set up the foreign key relationship in your screenshot.
I'll post only the main part. I have two tables, each one has to have the PK of the other as a FK.
CREATE TABLE apartment
(
cod_apartment INT NOT NULL PRIMARY KEY,
cod_offer INT NOT NULL
);
CREATE TABLE offer
(
cod_offer INT NOT NULL PRIMARY KEY,
cod_apartment INT NOT NULL
);
First I inserted the values on both tables and it was working, I could even search using "select * from...". But then I tried to add the foreign key:
This worked.
ALTER TABLE offer
ADD FOREIGN KEY (cod_apartment ) REFERENCES apartment;
And this not.
ALTER TABLE apartment
ADD FOREIGN KEY (cod_offer) REFERENCES offer;
This is the error message:
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint "FK__apartment__cod_offer__6383C8BA". The conflict occurred in database "kleber_apartment", table "dbo.offer", column 'cod_offer'.
The problem is, every time I try to execute, the FK name changes. And this FK actually doesn't exist. I already dropped both tables and tried to insert the values again, but the same happens.
What could be?
That means you're trying to add a foreign key when existing data doesn't obey that constraint. So you have a record in your apartment table where the cod_offer column does not match any value in the cod_apartment table.
Adding a foreign key not only constrains future data, but it requires that any existing data must also follow the rule.
And regarding the 6383C8BA, whenever you add a constraint without giving it a name, SQL Server picks one for you. Personally, I'd recommend something like:
alter table dbo.apartment
add constraint FK_apartment__cod_offer
foreign key (cod_offer) references dbo.offer (cod_offer);
This lets you define names the way you want, and is a little more clear about what you're actually building.
when I design a database for production, I got a problem.
I have 5 table's Product, SemiProduct, BOOM,BOOM_Details,Material.
Product(Code,Name,BOOM_Code,etc....)
SemiProduct(Code,Name,BOOM_Code,etc...)
BOOM(BOOM_Code,etc...)
BOOM_Details(ID,BOOM_Code,Component, Percent)
Material(Code,Name, etc..)
My data for each table is :
Product
{Pro1,Product1, BOOMPRO1}
{Pro2,Product2, BOOMPRO2}
-----------
SemiProduct
{SemiPro1,Semi Product1, BOOMSemi1}
{SemiPro2,Semi Product2, BOOMSemi2}
------------
BOOM
{BOOMPRO1}
{BOOMPRO2}
{BOOMSemi1}
{BOOMSemi2}
----------
Material
{M1,Material1}
{M2,Material12}
---------------
BOOM_Details
{1,BOOMPRO1,M1, 20}
{2,BOOMPRO1,M2, 25}
{3,BOOMPRO1,SemiPro1, 25}
{4,BOOMPRO1,SemiPro2, 30}
{5,BOOMPRO2,M1, 20}
{6,BOOMPRO2,M2, 25}
{7,BOOMPRO2,SemiPro1, 55}
The problem is col [Component] in [BOOM_Details].
It can be code of Material or Code of SemiProduct.
Please help me create FOREIGN KEY from Component REFERENCES to [Material].[Code] and [SemiProduct].[Code]
Or show me a different way to design the table with data like that.
Thank you very much !
This is a common SQL Anti-Pattern. You should change your table structures so that your Material and Code of SemiProduct tables have a column that is a foreign key to the BOOM_Details table. That way you can always join between the tables as needed.
So instead of a field in BOOM_Details that could point to either of the two tables, have a field in both of the tables that contains the primary key of the BOOM_Details table and is constrained by a foreign key constraint.
Foriegn key:- A FOREIGN KEY is a column which is used to join two tables. It points to a PRIMARY KEY in another table which we need to join. Here is the example for better understanding.
Read this for better understanding
Coming to the problem:- Here you need the foreign key between Boom_details and Material.So first you have to make sure that there is a primary key(ex:-id column with sequential no. id[1,2,3,4,5] or sequential alphabets[a,b,c,d] etc..) in the first table to which we have to point! Then add the foreign key column in your table from which we are pointing with same set of values as primary key in the first table.
EDIT:-
Here are the links for understanding how to use foreign key across multiple tables
LINK 1
LINK 2
Hope this helps!
I have a SQL database opened with visual studio, and I need to add some constraints to a table already created. I need a foreign key, which already has a foreign key from a third table. To explain better ,
Table ANIMALI needs a foreign key from table GABBIA, which has already a foreign key from table STANZA. This was the code I came up with:
ALTER TABLE ANIMALE ADD CONSTRAINT REF_ANIMA_GABBI_FK FOREIGN KEY (n_stanza, n_gabbia) REFERENCES GABBIA(n_stanza, n_gabbia);
This gives me an error, n_stanza is a column id not valid. I think it's about the fact that the ID for the class GABBIA is taken from joining n_gabbia and n_stanza, the latter being a key in class STANZA.
Can anyone help me out?
In order for your ALTER TABLE statement to work as written, both tables (not classes) "ANIMALE" and "GABBIA" must include the columns "n_stanza" and "n_gabbia".
In addition, in the table "GABBIA", there must be either a primary key constraint or a unique constraint on the pair of columns "n_stanza" and "n_gabbia". That is, you need something like either primary key (n_stanza, n_gabbia) or unique (n_stanza, n_gabbia) in the table "GABBIA".
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