I'm new to SQL so I'm likely asking a question with a very obvious answer. I'm making a simple database for phone plans, my tables, in order, are:
COUNTRY, PROVIDER, PHONE, PLAN, CUSTOMER.
They all have one primary key, and except for COUNTRY all have foreign keys referencing to the previous table.
My issue arises when inserting values into the PHONE table. These are the PROVIDER and PHONE tables:
CREATE TABLE Provider_T(
Name VARCHAR(25),
Provider_ID CHAR(10) NOT NULL,
Country_Abbrev CHAR(3) DEFAULT NULL,
Website VARCHAR(50) DEFAULT NULL,
CService_Number VARCHAR(15) DEFAULT NULL,
CONSTRAINT Provider_T_PK PRIMARY KEY(Provider_ID),
CONSTRAINT Country_Abbrev_FK FOREIGN KEY(Country_Abbrev) REFERENCES Country_T(Abbreviation));
CREATE TABLE Phone_T(
Phone_Model VARCHAR(25) NOT NULL,
Provider_ID CHAR(3) NOT NULL,
Smartphone BOOLEAN,
CONSTRAINT Phone_Model_PK PRIMARY KEY(Phone_Model),
CONSTRAINT Provider_ID_FK FOREIGN KEY(Provider_ID) REFERENCES Provider_T(Provider_ID));
This is my insert for the PHONE table:
INSERT INTO Phone_T(Phone_Model, Provider_ID, Smartphone) VALUES ("Nexus 5", "ROG", TRUE);
INSERT INTO Phone_T(Phone_Model, Provider_ID, Smartphone) VALUES ("Nexus 5", "KOD", TRUE);
I know I have duplicate Primary Keys, I'm stumped on how I could make one Phone Model for multiple PROVIDERS. I would love some advice and any help is appreciated.
Related
I have multiple tables and they all seem to be fine but there is this one table which I'm trying to create but it wont work because I am keep on getting Error1005 "Foreign key constraint is incorrectly formed".
These are the two tables. I don't know what seems to be the problem.
CREATE TABLE Patient(
ID INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Name VARCHAR(255) NOT NULL,
Age TINYINT UNSIGNED,
Sex VARCHAR(10),
Contact INT(11),
Email TEXT(2083),
PRIMARY KEY(ID)
);
CREATE TABLE Appointments (
Appointment_No INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Name VARCHAR(255) NOT NULL,
Contact INT(11),
Date DATE NOT NULL,
Time TIME NOT NULL,
Reason TEXT(2083),
PRIMARY KEY(Appointment_No),
FOREIGN KEY (Name, Contact) REFERENCES Patient (Name, Contact)
);
As per me, table structure should be like below:
CREATE TABLE Patient(
ID INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Name VARCHAR(255) NOT NULL,
Age TINYINT UNSIGNED,
Sex VARCHAR(10),
Contact INT(11),
Email TEXT(2083),
PRIMARY KEY(ID)
);
CREATE TABLE Appointments (
Appointment_No INT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE,
Patient_ID INT UNSIGNED NOT NULL,
Date DATE NOT NULL,
Time TIME NOT NULL,
Reason TEXT(2083),
PRIMARY KEY(Appointment_No),
FOREIGN KEY (Patient_ID) REFERENCES Patient (ID)
);
FOREIGN KEY (Name, Contact) REFERENCES Patient (Name, Contact)
The referenced columns in the Patient table must be part of a key. Ideally you would want Patient (Name, Contact) to be a unique key, because then the foreign key is guaranteed to reference exactly one row in the Patient table.
But in your table definition, the Name and Contact columns are not part of a key. That explains why you got the error given your table design.
But your table design is not good. Name and Contact are not good choices as a unique key, because two people can share a name, and in theory you could even have two people with the same name with the same contact details (for example, the former boxer George Foreman named his five sons George).
#Shadow is correct that it's a better idea is to reference Patient(id) instead, because it's guaranteed to be unique already.
Define Engine so sql statement would end with
ENGINE = MyISAM;
It should fix the issue.
Try to split the two foreign keys in two lines like this:
FOREIGN KEY (Contact) REFERENCES Patient (Contact)
FOREIGN KEY (Name) REFERENCES Patient (Name)
So I don't understand why I cannot insert data in my table that have foreign constraint keys or even modify anything in it.
Here is an example of the tables that are created. I am trying to insert data in the addresses table:
///////////////////////ADDRESSES TABLE ////////////////////////
CREATE TABLE IF NOT EXISTS addresses (
id INT NOT NULL AUTO_INCREMENT,
addressline1 VARCHAR(255) NOT NULL,
addressline2 VARCHAR(255) NOT NULL,
postcode VARCHAR(255) NOT NULL,
phonenumber INT(13) NOT NULL,
country_id INT NOT NULL,
PRIMARY KEY (id),
FOREIGN KEY (country_id) REFERENCES countries(id)
ON UPDATE CASCADE
ON DELETE RESTRICT
) ENGINE=InnoDB ";
///////////////////////COUNTRIES TABLE ////////////////////////
CREATE TABLE IF NOT EXISTS countries (
id INT NOT NULL AUTO_INCREMENT,
countryname VARCHAR(255) NOT NULL,
PRIMARY KEY (id)
)
The issue here is that you are trying to insert into a referencing table (addresses) when the referenced entry (the country you reference) does not exist. That's what's triggering the FOREIGN KEY CONSTRAINT exception.
Try first inserting some countries into the countries table, then inserting some addresses where you reference those countries you entered in the first step.
As for your second question, that's a choice for you to make. I would probably choose to have the User have an Address (address field in the User table), but some of that depends on how the data is being used/updated.
Have a quick look through this resource if you're new to relational database design. It covers (in brief) topics like relationship types, key constraints, and normal forms.
I'm new to both this site and databases. I am creating a database for a point of sale for a company. Im having problems since I have so many composite primary keys okay so here is my question... I have the table member:
DROP TABLE IF EXISTS member;
CREATE TABLE member (
fName varchar(10) NOT NULL,
lname varchar(10) NOT NULL,
shippingAddress varchar(50) NOT NULL,
billingAddress varchar(50) NOT NULL,
memberNo varchar(15) NOT NULL,
memStartDate date NOT NULL,
memOf varchar(15) ,
PRIMARY KEY(memberNo, shippingAddress)
);
and table shipping:
DROP TABLE IF EXISTS shipping;
CREATE TABLE shipping (
company varchar(10) NOT NULL,
warehouseAddress varchar(50) NOT NULL,
memberAddress varchar(50) NOT NULL,
memberNum varchar(15) NOT NULL,
orderNumber varchar(20) NOT NULL,
PRIMARY KEY(orderNumber)
);
ALTER TABLE shipping ADD CONSTRAINT shipping_memberAddnNUM_refs_member_memberNoNshippingAddress FOREIGN KEY (memberAddress, memberNum)
REFERENCES member (shippingAddress, memberNo);
So it gives me an errno: 150
I dont necessarily need member(shippingAddress) to be part of the primary key. But i do need to reference it my shipping table. Does anyone know how to get past this I have been looking at examples online but none of them seem to fix it.
I do it like this:
CONSTRAINT NAME_OF_PK PRIMARY KEY(Field1, Field2)
But this is Microsoft's SQL way of doing things.
You have the two columns in reverse order - from how they appear in the PRIMARY KEY of member. Try this:
ALTER TABLE shipping
ADD CONSTRAINT shipping_memberAddnNUM_refs_member_memberNoNshippingAddress
FOREIGN KEY (memberNum, memberAddress)
REFERENCES member (memberNo, shippingAddress);
I have three tables:
CREATE TABLE Address (
ResidentID CHAR(5) NOT NULL,
Location varchar(255) NOT NULL,
KEY ResidentID(ResidentID)
);
CREATE TABLE Customer (
CustomerID CHAR(5) NOT NULL,
ContactName varchar(40) NOT NULL,
PRIMARY KEY (CustomerID)
);
CREATE TABLE Supplier (
SupplierID CHAR(5) NOT NULL,
SupplierName varchar(40) NOT NULL,
PRIMARY KEY (SupplierID)
);
I want to store CustomerID and SupplierID in the Address.ResidentID field with using of foreign keys:
ALTER TABLE Address ADD CONSTRAINT fk_CustomerID1 FOREIGN KEY(ResidentID) REFERENCES Customer(CustomerID);
ALTER TABLE Address ADD CONSTRAINT fk_SupplierID1 FOREIGN KEY(ResidentID) REFERENCES Supplier(SupplierID);
But second 'ALTER TABLE' raises Error: relation already exists
Any suggestions?
Data example:
CustomerID ContactName
C0001 Den
SupplierID ContactName
S0001 John
So Address table should contains:
ResidentID Location
C0001 Alaska
S0001 Nevada
You need to either reference addresses from the Customer / Supplier (if they only have one) or two different columns.
The reason you see in this SQLFiddle You cannot INSERT the required columns into the Address table if the ResidentID references BOTH tables. You could only insert lines that would match the contents of Customer AND Supplier but you want an OR connection that you can't create that way.
(Note: In my solutions I assume addresses to be optional. As Tom pointed out in the comments that may not be what you wanted, or expected. Make sure to mark the FK Columns in the first solution as NOT NULL if you want addresses to be mandatory, its more complicated for the second one. You have to mind the correct insertion order then.)
Either:
CREATE TABLE Address (
AddressID CHAR(5) NOT NULL,
Location varchar(255) NOT NULL,
PRIMARY KEY (AddressID)
);
CREATE TABLE Customer (
CustomerID CHAR(5) NOT NULL,
AddressID CHAR(5),
ContactName varchar(40) NOT NULL,
PRIMARY KEY (CustomerID)
);
CREATE TABLE Supplier (
SupplierID CHAR(5) NOT NULL,
AddressID CHAR(5),
SupplierName varchar(40) NOT NULL,
PRIMARY KEY (SupplierID)
);
ALTER TABLE Customer ADD CONSTRAINT fk_AddressID_Cust FOREIGN KEY(AddressID) REFERENCES Address(AddressID);
ALTER TABLE Supplier ADD CONSTRAINT fk_AddressID_Supp FOREIGN KEY(AddressID) REFERENCES Address(AddressID);
or
CREATE TABLE Address (
CustomerID CHAR(5),
SupplierID CHAR(5),
Location varchar(255) NOT NULL,
PRIMARY KEY (CustomerID, SupplierID)
);
CREATE TABLE Customer (
CustomerID CHAR(5) NOT NULL,
ContactName varchar(40) NOT NULL,
PRIMARY KEY (CustomerID)
);
CREATE TABLE Supplier (
SupplierID CHAR(5) NOT NULL,
SupplierName varchar(40) NOT NULL,
PRIMARY KEY (SupplierID)
);
ALTER TABLE Address ADD CONSTRAINT fk_CustomerID1 FOREIGN KEY(CustomerID) REFERENCES Customer(CustomerID);
ALTER TABLE Address ADD CONSTRAINT fk_SupplierID1 FOREIGN KEY(SupplierId) REFERENCES Supplier(SupplierID);
The approach you're trying is (a) not possible and (b) undesirable even if it was possible.
The best approach is to have a CustomerAddress table and a SupplierAddress table, each with a single FK to the matching base table; or if you must, a cross-reference table with appropriate constraints.
If your motivation for having a single Address table was code reuse, you can still do that ... think in terms of a template xxxAddress table design that can refer to any base xxx table. You can write non-database code that treats the base table name as a parameter and then could handle any number of xxxAddress tables as you add more base tables over time.
Or if your motivation for having a single Address table was to simplify reporting, you can always create a view or stored proc that returns a union of all such tables + an added field to indicate the base table for each address row.
Angelo I am revising this a bit based on your comment ---
Angelo, I ran your sample code in a local MySQL instance (not SQLFiddle) and observed an error.
I was surprised (you learn something every day) that MySQL did allow two foreign key constraints to be defined on the same field; however when you attempt to insert data, when trying to point the FK to the Customer table, I get an error saying a foreign key constraint fails referencing the Supplier table; and vice versa for the insert trying to point the FK to the Supplier table.
So my revised statement is (a) it is possible to create the hydra-headed FK in at least some DBMSs -- verified in MySQL, MS SQL Server and Oracle -- although (b) this only makes sense to use when the foreign key can refer to the same logical entity by ID across multiple tables (e.g. to ensure there is a corresponding record in all required tables, for example); and (c) if used to refer to multiple tables where the primary key is NOT the same logical entity, only works if by chance the same primary key value just happens to exist in all referenced tables, which is likely to lead to subtle, hard-to-find errors.
In other words, your example would work when attempting to insert a record referring to Customer ID=3 only if there was also a Supplier ID=3, which are really logically unrelated.
So my slightly revised answer to the OP is, what you're trying to do is not possible (or logical) when the foreign key is referring to different ENTITIES, as in the OP example of Customers and Suppliers.
I have the following tables (Primary key in bold. Foreign key in Italic)
Customer table
ID---Name---Balance---Account_Name---Account_Type
Account Category table
Account_Type----Balance
Customer Detail table
Account_Name---First_Name----Last_Name---Address
Can I have two foreign keys in the Customer table and how can I implement this in MySQL?
Updated
I am developing a web based accounting system for a final project.
Account Category
Account Type--------------Balance
Assets
Liabilities
Equity
Expenses
Income
Asset
Asset_ID-----Asset Name----Balance----Account Type
Receivable
Receivable_ID-----Receivable Name-------Address--------Tel-----Asset_ID----Account Type
Receivable Account
Transaction_ID----Description----Amount---
Balance----Receivable_ID----Asset_ID---Account Type
I drew the ER(Entity relationship) diagram using a software and when I specify the relationship it automatically added the multiple foreign keys as shown above. Is the design not sound enough?
create table Table1
(
id varchar(2),
name varchar(2),
PRIMARY KEY (id)
)
Create table Table1_Addr
(
addid varchar(2),
Address varchar(2),
PRIMARY KEY (addid)
)
Create table Table1_sal
(
salid varchar(2),`enter code here`
addid varchar(2),
id varchar(2),
PRIMARY KEY (salid),
index(addid),
index(id),
FOREIGN KEY (addid) REFERENCES Table1_Addr(addid),
FOREIGN KEY (id) REFERENCES Table1(id)
)
Yes, MySQL allows this. You can have multiple foreign keys on the same table.
Get more details here FOREIGN KEY Constraints
The foreign keys in your schema (on Account_Name and Account_Type) do not require any special treatment or syntax. Just declare two separate foreign keys on the Customer table. They certainly don't constitute a composite key in any meaningful sense of the word.
There are numerous other problems with this schema, but I'll just point out that it isn't generally a good idea to build a primary key out of multiple unique columns, or columns in which one is functionally dependent on another. It appears that at least one of these cases applies to the ID and Name columns in the Customer table. This allows you to create two rows with the same ID (different name), which I'm guessing you don't want to allow.
Yes, a table have one or many foreign keys and each foreign keys hava a different parent table.
CREATE TABLE User (
user_id INT NOT NULL AUTO_INCREMENT,
userName VARCHAR(100) NOT NULL,
password VARCHAR(255) NOT NULL,
email VARCHAR(255) NOT NULL,
userImage LONGBLOB NOT NULL,
Favorite VARCHAR(255) NOT NULL,
PRIMARY KEY (user_id)
);
and
CREATE TABLE Event (
EventID INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY (EventID),
EventName VARCHAR(100) NOT NULL,
EventLocation VARCHAR(100) NOT NULL,
EventPriceRange VARCHAR(100) NOT NULL,
EventDate Date NOT NULL,
EventTime Time NOT NULL,
EventDescription VARCHAR(255) NOT NULL,
EventCategory VARCHAR(255) NOT NULL,
EventImage LONGBLOB NOT NULL,
index(EventID),
FOREIGN KEY (EventID) REFERENCES User(user_id)
);