The columns in 'table_XXX' do not match an existing primiary key or UNIQUE constraint - sql

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.

Related

How to make sure that both column values exists only once in database table?

I have a table which stores the hash tags as a many to many relation ship
Tags Table
userID - Foreign key
tags - foreign key
I have used Unique constraint which I think is a foolish one.
Here I want to ensure that a user uses the tag a user uses each tag only once in that table.
What query will suit this scenario?
So the desired output is like a user uses only one tag
The database I use is PostgreSQL.
Since I use Django where I have the code below
user = models.ForeignKey("User",unique=True)
userTags = models.ForeignKey("Tags",unique=True)
which has a meaning of that
user column is foreign key reference from User table and it's a unique column
UserTags column is a foreign key reference from Tags table and that column is unique

SQL relation 1 key not 2 keys between tables

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.

Using foreign keys in a SQL table

I'm trying to reference a foreign key in a table to reference the primary key of another in order to get an attribute from that table. I think I worded that right.
It looks more obvious what I"m trying to do when you look at the code.
SELECT PATIENT_T.FIRST_NAME, PATIENT_T.LAST_NAME, TREATMENT_TYPE
FROM TREAMENT;
Where Patient_T is another table, where the primary key is PATIENT_ID.
Treatment is the table I'm searching from, where Treatment_ID is the primary key of that, and treatment type is another attribute.
Treatment has PATIENT_ID as a foreign key, so I thought that meant I could reference the first and last name by some sort of reference.
Did I type it wrong or how exactly do i do this?

Try like below
SELECT PATIENT_T.FIRST_NAME, PATIENT_T.LAST_NAME, TREATMENT_TYPE FROM TREAMENT
LEFT JOIN Patient_T.PATIENT_ID = TREAMENT.PATIENT_ID

Adding Constraint with multiple foreign keys

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".

SQL Server 2008: The columns in table do not match an existing primary key or unique constraint

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