The candidates for primary key are name=(lastName, firstName), phoneNumber, Address1=(address, city, state), Address1=(address, zipCode). Let's illustrate with an example: a table customers contains columns lastName, firstName, phoneNumber, address, city, state, zipCode. You should use as few columns as possible. But it could also make up of several columns. Primary key is usually a single column (e.g., customerID or productCode).Unlike factual information such as phone number, fact-less number is ideal for primary key, as it does not change. This arbitrary number is fact-less, as it contains no factual information. Most RDBMSs support so-called auto-increment (or AutoNumber type) for integer primary key, where (current maximum value + 1) is assigned to the new record. Primary key could take an arbitrary number.However, it is best to use numeric column as primary key for efficiency. But it could also be other types, such as texts. Primary key often uses integer (or number) type.For example, phoneNumber may not be appropriate to be used as primary key for table Customers, because it might change. If you change its value, you have to change all its references otherwise, the references will be lost. Primary key is used to reference other tables. The value of the primary key should not change.The primary key shall be simple and familiar, e.g., employeeID for employees table and isbn for books table.In other words, it shall not contain NULL.Ĭonsider the followings in choose the primary key: The primary key shall always have a value.For example, customerName may not be appropriate to be used as the primary key for the Customers table, as there could be two customers with the same name. The values of primary key shall be unique (i.e., no duplicate value).The decision may not be straight forward but the primary key shall have these properties: You have to decide which column(s) is to be used for primary key. The primary key is also used to reference other tables (to be elaborated later). Most RDBMSs build an index on the primary key to facilitate fast search and retrieval. A primary key is called a simple key if it is a single column it is called a composite key if it is made up of several columns.
For example, an unique number customerID can be used as the primary key for the Customers table productCode for Products table isbn for Books table. To ensure uniqueness, each table should have a column (or a set of columns), called primary key, that uniquely identifies every records of the table. In the relational model, a table cannot contain duplicate rows, because that would create ambiguities in retrieval.
Divide the data into subject-based tables.Ĭhoose one column (or a few columns) as the so-called primary key, which uniquely identify the each of the rows. Once you have decided on the purpose of the database, gather the data that are needed to be stored in the database. Step 2: Gather Data, Organize in tables and Specify the Primary Keys Gather the requirements and define the objective of your database, e.g.ĭrafting out the sample input forms, queries and reports, often helps. Step 1: Define the Purpose of the Database (Requirement Analysis) Guidelines (usually in terms of what not to do instead of what to do) are provided in making these design decision, but the choices ultimately rest on the you - the designer. No two customized applications are alike, and hence, no two database are alike. Databases are usually customized to suit a particular application. This is because duplicate data not only waste storage spaces but also easily lead to inconsistencies.ĭatabase design is more art than science, as you have to make many decisions.
Idatabase relational free#
There are also many free and open-source RDBMS, such as MySQL, mSQL (mini-SQL) and the embedded JavaDB (Apache Derby).Ī relational database organizes data in tables (or relations). Today, there are many commercial Relational Database Management System (RDBMS), such as Oracle, IBM DB2 and Microsoft SQL Server. It has since become the dominant database model for commercial applications (in comparison with other database models such as hierarchical, network and object models). Relational database was proposed by Edgar Codd (of IBM Research) around 1969.
A Quick-Start Tutorial on Relational Database Design Introduction
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