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VOOZH | about |
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VOOZH | about |
By Mark Drake
Manager, Developer Education
When designing a database, there may be times when you want to put limits on what data is allowed in certain columns. For example, if you’re creating a table that will hold information on skyscrapers, you may want the column holding each building’s height to prohibit negative values.
Relational database management systems (RDBMSs) allow you to control what data gets added to a table with constraints. A constraint is a special rule that applies to one or more columns — or to an entire table — that restricts what changes can be made to a table’s data, whether through an INSERT, UPDATE, or DELETE statement.
This article will review in detail what constraints are and how they’re used in RDBMSs. It will also walk through each of the five constraints defined in the SQL standard and explain their respective functions.
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Structured Query Language — commonly known as SQL — is a language used to define, control, manipulate, and query data held in a relational database. SQL has been widely adopted since it was first developed in the 1970s, and today it’s the predominant language used to manage relational database management systems.
Ideal for managing structured data (data that can fit neatly into an existing data model), SQL is an essential tool for developers and system administrators in a wide variety of contexts. Also, because of its maturity and prevalence, candidates with SQL experience are highly sought after for jobs across a number of industries.
This series is intended to help you get started with using SQL. It includes a mix of conceptual articles and tutorials which provide introductions to various SQL concepts and practices. You can also use the entries in this series for reference while you continue to hone your skills with SQL.
Note: Please be aware that the tutorials in this series use MySQL in examples, but many RDBMSs use their own unique implementations of SQL. Although the commands outlined in this tutorial will work on most RDBMSs, the exact syntax or output may differ if you test them on a system other than MySQL.
Browse Series: 27 tutorials
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Former Technical Writer at DigitalOcean. Focused on SysAdmin topics including Debian 11, Ubuntu 22.04, Ubuntu 20.04, Databases, SQL and PostgreSQL.
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I’d like to say it’s one of the best articles I’ve ever seen in this topic of constraints in sql , keep it up authors
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