SQL: “sequel”; Structured Query Language) is a domain-specific language 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). It is particularly useful in handling structured data, i.e. data incorporating relations among entities and variables.
SQL offers two main advantages over older readwrite APIs such as ISAM or VSAM. Firstly, it introduced the concept of accessing many records with one single command. Secondly, it eliminates the need to specify how to reach a record, e.g. with or without an index.
Originally based upon relational algebra and tuple relational calculus, SQL consists of many types of statements, which may be informally classed as sublanguages, commonly: a data query language (DQL), a data definition language (DDL), a data control language (DCL), and a data manipulation language (DML). The scope of SQL includes data query, data manipulation (insert, update and delete), data definition (schema creation and modification), and data access control. Although SQL is essentially a declarative language (4GL), it also includes procedural elements.
SQL was one of the first commercial languages to use Edgar F. Codds relational model.Use SQL
1 – ‘SQL’ is usually pronounced ‘S-Q-L’ (Structured Query Language).
2 – There are various dialects of SQL but the most widely used database engines today adhere to the SQL99 standard from ANSI, and many vendors have implemented extra features to extend that standard (the Microsoft ‘flavor’ of SQL is called T-SQL or Transact-SQL, the Oracle version is PL/SQL).
3 – Getting the Data Out!
4 – A simple example would be something like:
5 – Queries are usually much more complicated than this.
6 – If we want to filter the rows returned by the select statement, a where clause is needed to qualify the record sets returned.
7 – INSERT and UPDATE statements are used to add and change data in an SQL database (check the links below for some excellent tutorials that can take you further).
8 – The DELETE statement is used to remove data from an SQL database.