SQL, stands for structured query language, is a domain-specific declarative programming language based on tuple relational calculus and relational algebra. It is used in programming and designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS).

RDBMS is a relational database management system and stores related data in database objects called table which consists of rows (aka Records) and columns (aka Fields).

RDSMS is a distributed, in-memory data stream management system that use SQL queries to process unstructured and structured data stream in real time.

History of SQL:

SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd in the early 1970s.
SQL became a standard of the American National Standards Institute (ANSI) in 1986 and of the International Organization for Standardization (ISO) in 1987. The recent version was published in 2016.

SQL Dialect:

The users request new features and capabilities that do not exist in the SQL standard yet, therefore, even with the SQL standard in place, there are many SQL dialects in various database products.

Because ANSI and ISO have not yet developed these important features, RDBMS vendors are free to invent their own new syntax structure.

The following are the most popular dialects of SQL:

• PL/SQL or procedural language/SQL is developed by Oracle for the Oracle Database.
• T-SQL or Transact-SQL is developed by Microsoft for Microsoft SQL Server.
• PL/pgSQL or Procedural Language/PostgreSQL that consists of SQL dialect and extensions implemented in PostgreSQL
• MySQL(acquired by ORACLE) has its own procedural language since version 5.