Introduction of SQL
SQL, short for Structured Query Language, which is a programming language to access and manipulate databases, meanwhile, it’s as one of ANSI standard. SQL is not only used to access & query data, but also to update and manage the relational database systems. Obviously, the latter function shows its strong performances of Structured Query Language and it’s what critical to administrators.
Statistics shows that SQL is the most important relational database manipulation language now. The influence of Structured Query Language is beyond the database field; it gets attention & adoption in other fields, such as data retrieval of artificial intelligence. Besides, SQL has be embedded in the fourth generation of software development tools.
Structured Query Language exists independently of database itself, and computer, network, operation system used. The SQL-based DBMS products can run in a wide range, from PC, workstation to a variety of computer operation systems (based on WLAN, Minicomputer, mainframe etc.). You can see its good scalability and portability.
Versions of SQL
Although SQL is an ANSI standard, there are different versions of the SQL language. In the beginning, it passed by the American National Standards Institute in October 1986. Then, the International Organization for Standardization (ISO) has issued a formal international standard SQL. In April 1989, ISO SQL89 standard had been proposed with integrity features. And the SQL92 standard was announced in November of 1992 & it divided database into three levels: base set, standard set and complete set.
There are subtle differences in a variety of databases for its support and standard to SQL. However, they all support at least the major commands (such as SELECT, UPDATE, DELETE, INSERT, WHERE) in a similar manner.
SQL language contains four parts:
Part One: SQL DDL, stand for Data Definition Language: it includes statements like CREATE, DROP, ALTER, etc.
Part Two: DML, stand for Data Manipulation Language, for example: INSERT statement, UPDATE statement and DELETE statement.
Part Three: Data Query Language, such as SELECT statement.
The last part: Data Control Language, for instance, GRANT, REVOKE, COMMIT, ROLLBACK and other statements.
What can Structured Query Language do
Structured Query Language can execute queries against a database;
Structured Query Language can not only retrieve, also insert and update records in a database;
Structured Query Language can delete records from a database;
Structured Query Language can create new tables in a database and even create new databases;
Structured Query Language can create stored procedures in a database;
Structured Query Language can create views in a database;
Structured Query Language can set permissions on tables, procedures, and views;