Database Design – Normalization of Library Book Table with Multiple Authors

database-designMySQLpostgresqlsql server

I have a database structure with two tables:

The first one is called Author, has two columns (AuthID, AuthName) and its Primary Key is (PK_AuthID).
The second one is called Book and has three columns (BookID, BookTitle, AuthID). Its Primary Key is (PK_BookID), and has (FK_AuthID) defined as a Foreign Key that referes to Author table.

The question is: If one Book has more than one Author, what is the best design pattern to follow in order to maintain the second Author, and at the same time keep the Book table without NULL values?

Best Answer

The only sensible design I can think of - since books can have 20 authors - is to always use a junction table and don't bother storing the AuthorID in the book table some of the time (and don't even think about storing a comma-separated list of AuthorIDs, please, or adding Author2, Author3, ... columns). This will just make queries complex.

BookAuthors(BookID (FK points to Book), AuthorID (FK points to Author))

In this case, you can remove the AuthID column from the Book table. Don't bother abbreviating to AuthID - you don't really think that makes you more productive or makes the code easier to read, do you?

Also, as a general rule, don't spend time trying to worry about how you will eliminate NULLs everywhere.

Related Solutions

Postgresql – postgres composite index design

I would try making two composite partial indexes like

CREATE INDEX idx1 ON tw_schedules (scenario_id, type_well_id) WHERE type_well_id IS NOT NULL;

CREATE INDEX idx2 ON tw_schedules (scenario_id, tw_import_id) WHERE tw_import_id IS NOT NULL;

But, of course, everything depends on the selectivity of these indexes.

Sql-server – Unique Constraint with multiple null columns

I think your database is suffering from a bad data model. You might want to rethink it a little, judging from the tables you've mentioned the model isn't well normalized and you're trying to enforce a foreign key reference to a table column which isn't really a key to anything. One way to go is something like this :

CREATE TABLE EMP (ID INT PRIMARY KEY IDENTITY
                 ,EmpName VARCHAR(100) NULL)

CREATE TABLE PCTypes (id INT PRIMARY KEY IDENTITY
                     ,PcTypeName VARCHAR(100) NULL)

CREATE TABLE PC (Id INT PRIMARY KEY IDENTITY
                ,EmpId INT NULL
                ,PCName VARCHAR(100) NULL
                ,HostName VARCHAR(100) NULL
                ,PhysicalLocation VARCHAR(100) NULL
                ,PCType INT NULL)

ALTER TABLE PC ADD CONSTRAINT FK_PC_EmpId FOREIGN KEY (empId) REFERENCES Emp(id)
ALTER TABLE PC ADD CONSTRAINT FK_PC_PCType FOREIGN KEY (PCType) REFERENCES PCTypes(id)

CREATE TABLE PCNetwork (Id INT PRIMARY KEY IDENTITY
                       ,NetworkName VARCHAR(100) NULL
                       ,EmpId INT NULL
                       ,PhysicalLocation VARCHAR(100) NULL)

ALTER TABLE PCNetwork ADD CONSTRAINT FK_PCNetwork_EmpId FOREIGN KEY (empId) REFERENCES Emp(id)

CREATE TABLE PCNetwork_PCs (PCNetworkId INT NOT NULL
                           ,PCId INT NOT NULL
                           ,IPAddr NVARCHAR(20) NULL)

ALTER TABLE PCNetwork_PCs ADD CONSTRAINT FK_PCNetwork_PCs_Network FOREIGN KEY (PCNetworkId) REFERENCES PCNetwork(id)
ALTER TABLE PCNetwork_PCs ADD CONSTRAINT FK_PCNetwork_PCs_PC FOREIGN KEY (PCId) REFERENCES PC(id)
CREATE UNIQUE INDEX uq_pcnetworks ON PCNetwork_PCs(PCNetworkId, PCId)
CREATE UNIQUE INDEX uq_pcnetworks_ip ON PCNetwork_PCs(IPAddr)

Best Answer

Related Solutions

Postgresql – postgres composite index design

Sql-server – Unique Constraint with multiple null columns

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