Structured Query Language (SQL)

SQL is a domain-specific language designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS).

SQL data incorporates relations among entities and variables.

Originally based upon relational algebra and tuple relational calculus, SQL consists of many types of statements,[6] which may be informally classed as sublanguages, commonly:

• data query language (DQL)
• data definition language (DDL) (schema creation and modification)
• data control language (DCL)
• data manipulation language (DML) (insert, update, and delete)

SQL is a declarative language (4GL) which also includes procedural elements.

SQL - wikipedia

SQL Syntax

The SQL language is subdivided into several language elements, including:

• Clauses, which are constituent components of statements and queries.
• Expressions, which can produce either scalar values, or tables consisting of columns and rows of data
• Predicates, which specify conditions that can be evaluated to SQL three-valued logic (3VL) (true/false/unknown) or Boolean truth values and are used to limit the effects of statements and queries, or to change program flow.
• Queries, which retrieve the data based on specific criteria. This is an important element of SQL.
• Statements, which may have a persistent effect on schemata and data, or may control transactions, program flow, connections, sessions, or diagnostics.
• SQL statements also include the semicolon (";") statement terminator. Though not required on every platform, it is defined as a standard part of the SQL grammar.
• Insignificant whitespace is generally ignored in SQL statements and queries, making it easier to format SQL code for readability.