Structured Query Language (SQL) (pronounced / ˌɛsˌkjuˈɛl / S-Q-L; or alternatively as / ˈsiːkwəl / ⓘ "sequel") [4][5] is a domain-specific language used to manage data, especially in a relational …

MySQL (/ ˌmaɪˌɛsˌkjuːˈɛl /) [6] is an open-source relational database management system (RDBMS). [6][7] Its name is a combination of "My", the name of co-founder Michael Widenius ' daughter My, [1] …

The basic unit of a PL/SQL source program is the block, which groups together related declarations and statements. A PL/SQL block is defined by the keywords DECLARE, BEGIN, EXCEPTION, and END. …

SQL injection is a common security vulnerability that arises from letting attacker-supplied data become SQL code. This happens when programmers assemble SQL queries either by string interpolation or …

PostgreSQL (/ ˈpoʊstɡrɛskjuˌɛl / ⓘ POHST-gres-kew-EL), [11][12] also known as Postgres, is a free and open-source relational database management system (RDBMS) emphasizing extensibility and SQL …

Database objects are permanent, [3] which means that they remain in their form as long as they are not explicitly changed or deleted. Application- or user-specific database objects in relational databases …

NoSQL (originally meaning " N ot o nly SQL " or "non-relational") [1] refers to a type of database design that stores and retrieves data differently from the traditional table-based structure of relational …

In SQL, null is a marker, not a value. This usage differs from most programming languages, where a null value of a reference means it is not pointing to any object.

In computer science, ACID (atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. …

A VARCHAR or variable character field is a set of character data of indeterminate length. The term varchar refers to a data type of a field (or column) in a database which can hold letters and numbers. …