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What is a Relational Database?

When most people think of databases they think of relational databases because for years they have been most popular type of database by a wide margin. A relational database is a database with multiple tables, and each table has rows of entries and columns with attribute names. Relational database can be thought of as a bunch of Microsoft Excel spreadsheets linked together. The advantage to having multiple tables over one extremely large table is that it is easier to deal with and makes more sense to group things logically.

When going about creating a relational database, it’s important to think about the schema. The schema is essentially the plan for a table. The schema details how everything will be laid out and relate to each other. Think of the schema as a blueprint for a table. Another important thing to know is some of the terminology that is special to relational databases. The technical name for a row in a database is tuple, but sometimes they are also referred to as records. Columns are technically attributes, but they are also called fields. A tuple/row spans all the attributes in a table and will be composed of multiple attributes. All of the entries in a table and the table itself are called a relation, hence the name “relational database”. A relational database usually has multiple tables because if you only need one table, then a database is probably overkill and you would be better off with a spreadsheet program, like Microsoft Excel.

Each entry in a table in a relational database has a primary key, which identifies it. A primary key has to be unique and it can’t change. A foreign key is an attribute for an entry in one table that corresponds to a primary key in another table. A foreign key links an entry to another table. Database tables can also be indexed to reduce the time searches and queries take. Indexes increase the storage space required to save a database and lengthen some operations like inserts and other actions that write to a hard disk, so they should only be used sparingly.

Since relational databases are so structured, it is relatively easy to get specific information out of them with a form of the structured query language (SQL). SQL commands instruct the database to return information that meets some criterion in the form of a table. The result is often referred to as a view or query result. Many relational databases have their own SQL language specifically made for it. Examples are Oracle’s MySQL and Microsoft’s MSSQL.

There are many relational database products available on the market. JDBC is a popular relational database that is written in Java and is specifically suited to work with Java programs. Most of the major software makers are also in the relational database market. IBM has multiple relational databases, one of which is IBM DB2. Microsoft has Microsoft SQL Server and Microsoft Access. Oracle has multiple software products and owns the extremely popular MySQL product, which is open source. Relational databases have even migrated to the cloud. Amazon now offers the Amazon Relational Database Service (RDS) as part of it Amazon Web Services (AWS) cloud computing platform.


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