What is a Database?A database is a phối of data stored in a computer. This data is usually structured in a way that makes the data easily accessible.

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What is a Relational Database?

A relational database is a type of database. It uses a structure that allows us to identify and access data in relation khổng lồ another piece of data in the database. Often, data in a relational database is organized into tables.

Tables: Rows & Columns

Tables can have hundreds, thousands, sometimes even millions of rows of data. These rows are often called records.

Tables can also have many columns of data. Columns are labeled with a descriptive name (say, age for example) & have a specific data type.

For example, a column called age may have a type of INTEGER (denoting the type of data it is meant khổng lồ hold).


In the table above, there are three columns (name, age, and country).

The name và country columns store string data types, whereas age stores integer data types. The mix of columns và data types 3d the schema of this table.

The table also has four rows, or records, in it (one each for Natalia, Ned, Zenas, and Laura).

What is a Relational Database Management System (RDBMS)?

A relational database management system (RDBMS) is a program that allows you khổng lồ create, update, & administer a relational database. Most relational database management systems use the SQL language khổng lồ access the database.

What is SQL?

SQL (Structured Query Language) is a programming language used to lớn communicate with data stored in a relational database management system. SQL syntax is similar khổng lồ the English language, which makes it relatively easy lớn write, read, and interpret.

Many RDBMSs use SQL (and variations of SQL) to lớn access the data in tables. For example, SQLite is a relational database management system. SQLite contains a minimal phối of SQL commands (which are the same across all RDBMSs). Other RDBMSs may use other variants.

(SQL is often pronounced in one of two ways. You can pronounce it by speaking each letter individually like “S-Q-L”, or pronounce it using the word “sequel”.)

Popular Relational Database Management Systems

SQL syntax may differ slightly depending on which RDBMS you are using. Here is a brief description of popular RDBMSs:


MySQL is the most popular xuất hiện source SQL database. It is typically used for website application development, và often accessed using PHP.

The main advantages of MySQL are that it is easy lớn use, inexpensive, reliable (has been around since 1995), và has a large community of developers who can help answer questions.

Some of the disadvantages are that it has been known khổng lồ suffer from poor performance when scaling, xuất hiện source development has lagged since Oracle has taken control of MySQL, & it does not include some advanced features that developers may be used to.


PostgreSQL is an xuất hiện source SQL database that is not controlled by any corporation. It is typically used for web application development.

PostgreSQL shares many of the same advantages of MySQL. It is easy lớn use, inexpensive, reliable and has a large community of developers. It also provides some additional features such as foreign key support without requiring complex configuration.

The main disadvantage of PostgreSQL is that it can be slower in performance than other databases such as MySQL. It is also slightly less popular than MySQL.

For more information about PostgreSQL including installation instructions, read this article.

Oracle DB

Oracle Corporation owns Oracle Database, & the code is not mở cửa sourced.

Oracle DB is for large applications, particularly in the banking industry. Most of the world’s vị trí cao nhất banks run Oracle applications because Oracle offers a powerful combination of technology & comprehensive, pre-integrated business applications, including essential functionality built specifically for banks.

The main disadvantage of using Oracle is that it is not không tính phí to use like its open source competitors và can be quite expensive.

SQL Server

Microsoft owns SQL Server. Lượt thích Oracle DB, the code is close sourced.

Large enterprise applications mostly use SQL Server.

Microsoft offers a miễn phí entry-level version called Express but can become very expensive as you scale your application.


SQLite is a popular xuất hiện source SQL database. It can store an entire database in a single file. One of the most significant advantages this provides is that all of the data can be stored locally without having to lớn connect your database khổng lồ a server.

SQLite is a popular choice for databases in cellphones, PDAs, MP3 players, set-top boxes, and other electronic gadgets. The SQL courses on nasaconstellation.com use SQLite.

For more info on SQLite, including installation instructions, read this article.

Using An RDBMS On nasaconstellation.com

On nasaconstellation.com, we use both SQLite & PostgreSQL. While this may sound confusing, don’t worry! We want to găng tay that the basic syntax you will learn can be used in both systems. For example, the syntax khổng lồ create tables, insert data into those tables, & retrieve data from those tables are all identical. That’s one of the nice parts of learning SQL — by learning the fundamentals with one RDBMS, you can easily begin work in another.

That being said, let’s take a look at some of the more subtle details:

File extensions — when working with databases on nasaconstellation.com, take a look at the name of the tệp tin you’re writing in. If your tệp tin ends in .sqlite, you’re using a SQLite database. If your tệp tin ends in .sql, you’re working with PostgreSQL.

Data types — You’ll learn about data types very early into learning a RDBMS. One thing to lưu ý is that SQLite và PostgreSQL have slightly different data types. For example, if you want to store text in a SQLite database, you’ll use the TEXT data type. If you’re working with PostgreSQL, you have many more options. You could use varchar(n), char(n), or text. Each type has its own subtle differences. This is a good example of PostgreSQL being slightly more robust than SQLite, but the core concepts remaining the same.

Built-in tables — As you work your way through more complicated lessons on databases, you’ll start to lớn learn how lớn access built-in tables. For example, if you take our lesson on indexes, you’ll learn how to lớn look at the table that the system automatically creates to keep track of what indexes exist. Depending on which RDBMS system you are using (in that lesson we’re using PostgreSQL), the syntax for doing that will be different. Any time you’re writing SQL about the database itself, rather than the data, that syntax will likely be unique to the RDBMS you’re using.

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Relational databases store data in tables. Tables can grow large & have a multitude of columns and records. Relational database management systems (RDBMSs) use SQL (and variants of SQL) to manage the data in these large tables. The RDBMS you use is your choice và depends on the complexity of your application.