I am using sql server management studio and I have two tables, "City" and "Booking". In the booking table, there are two columns, "SourceCity" and "DestinationCity". I want to take two foreign keys from city table to Booking table for the above mentioned columns, but I don't know how to do it. I want to use this all for a stored procedure for adding new bookings as well. please help me out here.
I guess, youcan try something like this:
ALTER TABLE Booking
ADD CONSTRAINT FK_BookingSourceCity
FOREIGN KEY (SourceCity)
REFERENCES City (CityName);
ALTER TABLE Booking
ADD CONSTRAINT FK_BookingDestinationCity
FOREIGN KEY (DestinationCity)
REFERENCES City (CityName);
I assume CityName is a primary key in the table City
Related
I have a table that I want to make which is a bridge table for teacher and class table. This is the ERD
I initially thought I'm going to create this table by
CREATE TABLE class_teacher
(
teacher_id number(3),
class_id number(2),
CONSTRAINT class_teacher_pk
PRIMARY KEY(teacher_id, class_id),
CONSTRAINT class_teacher_teacher_fk
FOREIGN KEY(teacher_id) REFERENCES teacher(teacher_id),
CONSTRAINT class_teacher_class_fk
FOREIGN KEY(class_id) REFERENCES class(class_id)
);
But on the web I see people just having two foreign keys and no primary key, or table with no foreign key and having a primary key for two columns.
Am I doing it incorrectly?
Am I doing it incorrectly?
No, it looks correct.
Although I would question the size of the numeric data types as you are restricted to only have 1999 teachers and 199 classes (including negative numbers); this may be enough for immediate use but after several years when classes get re-organised or when the syllabus is re-written and new classes are created then you may run out of primary keys.
Does create statement returns any error? Otherwise you should be good.
Try to insert some data in all 3 tables and run some delete statements to see how it goes.
I am structuring a postgres database.
I have two tables, products (coke) and optional (with ice, lemon ...), that is, a relationship many to many.
An associative table is usually built using the primary keys of the tables, correct? However, in my case, there is a specific feature ... due to some imports from other databases...I have two ids fields (id and "externalId"), one primary key and one common ... one is the local id of my bank and the other represents the id that the item has in the bank from which it was imported.
I need an associative table between "externalId" and a primary key from another table.
ExternalId is not a primary key...
ALTER TABLE public.opcional_produto
Add
CONSTRAINT idproduto_fkey FOREIGN KEY (prod_id) REFERENCES public.produto (prod_idExt)
ERROR: there is no unique constraint matching given keys for
referenced table "produto" SQL state: 42830
How can I do?
If externalid is unique, you should create a unique constraint:
ALTER TABLE produto ADD UNIQUE (externalid);
Ideally it should also be not nullable:
ALTER TABLE produto ALTER externalid SET NOT NULL;
Now it can be used as target of a foreign key.
Here is an example of what I need, different values:
I already have table 1 created in the database.
Table 1: Person
Columns: PK->ID, Name, Favorite Color, Favorite Sport, etc..
This table is already in database and filled with values.
Now I want to create a second table, Table 2 which has a primary key of Favorite Sport column from my Table 1 and just one more column for the description.
Ex:
Table 2: Sports
Columns: Pk->Favorite Sport, description
I want to make sure I am just creating this table correctly, so I don't mess anything up. Would this be the correct syntax to use? (I will fill up the data separately after table is created.)
CREATE TABLE Sports (
Favorite_Sport Varcher(25),
Description Varcher(100),
PRIMARY KEY(Favorite_Sport),
Foreign KEY(Favorite_Sport) REFERENCES Person;
)
Thanks!
There are probably several ways to do this, but I think I'd go with
CREATE TABLE Sports
(SPORT Varchar2(25)
CONSTRAINT PK_SPORTS
PRIMARY KEY
USING INDEX,
Description Varchar2(100));
(I changed the name of the primary key column on the SPORTS table to SPORT).
You really don't want nor can you have SPORTS.SPORT reference PERSON.FAVORITE_SPORT, as FAVORITE_SPORT is not a primary or unique key on PERSON. Instead, you want the foreign key relationship to go the other way around, with PERSON.FAVORITE_SPORT referencing SPORTS.SPORT:
ALTER TABLE PERSON
ADD CONSTRAINT PERSON_FK1
FOREIGN KEY (FAVORITE_SPORT) REFERENCES SPORTS(SPORT);
SQLFiddle here
Best of luck.
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 have the following datatypes - House, Owner, with the primary keys houseID and ownerID respectively.
An Owner can have many Houses. And a House can Have many Owners. So I created an intermediate table HouseOwner that contains two columns, houseID and ownerID.
Should I make the houseID and ownerID columns a joint primary key for the HouseOwner table?
What about creating relationships between the HouseOnwer table and the House and Owner tables, I go to Database Diagrams and add all three tables - Now should I drag houseID from the House table onto houseID from the HouseOwner table? Or should do it the other round and drag houseID from the HouseOwner table to houseID on the House table? I am unsure of which way to do it as the dialog that pops up is looking for a Primary key table and a Foreign key table.
1) Yes - Specifically, I'd do this because if you use some ORM tools (specifically EF), the many-to-many relationship would be automatically figured out when your tables are designed like this.
2) I'd suggest just doing it the old fashioned way, so you don't have to worry about the UI:
alter table HouseOwner
add constraint FK_HouseOwner_House
foreign key (HouseId)
references House (HouseId)
go
alter table HouseOwner
add constraint FK_HouseOwner_Owner
foreign key (OwnerId)
references Owner (OwnerId)
go
Question 1: I would add an additional surrogate primary key (just an identity column) but there are a lot of discussions about this.
Question 2: the foreign keys are in your HouseOwner table and they relates to the PK of house and the other foreign key to the owner table.