SQL:- it stands for structured query language. It was introduced by Donald D. Chamberlain and Raymond F. Boycee in 1974. It obeys ISO/IEC standard. It is special purpose programming language, which works on RDBMS. SQL is relational algebra and touple calculus based language. In present SQL is used for communication through data base. SQL is standard back end programming language. SQL is case - insensitive language. It means SQL command may be written in both capital (upper level) and small (lower level) letters. User can create objects of data base using SQL commands, ca perform all types of constraints, can manipulate data, can control transaction. SQL is used in all types of DBMS software like - Oracle, MySQL, DB2, SQL server, sybase, ingress, Fox pro, MS ACCESS, libre office base etc.SQL is free form language. It means there is no need to write commands of this language in special format SQL was firstly include in form of commercial language for "A relational model of data for large shared data bankers" in relational mode 1970, research paper of E.F. codd.
Characteristics/importance of SQL:-
1. Statements of this language are similar to English language so it is easy to read-write query and understand.
2. SQL statement can written by those users who has no knowledge of programming language so there is many users of SQL.
3. SQL is procedural programming language so it has no definite structure.
4. SQL is case-in sensitive language. It means SQL query may be written in both small and capital letters.
5. There are many ways to write SQL statement but it provide similar result.
6. SQL is flexible language. It means SQL command may be in any place (any row or column) in any program. With it, it can be added with other programming language.
7. SQL is very popular and universal data base language, which complete all the operations performed on RDBMS.
Classification of SQL Commands:-
SQL commands are divided in following four parts -
1. DDL (Data Definition Language)
Create, alter, drop, rename , describe.
2. DML (Data Manipulating Language)
Insert, update, delete.
3. DCL (Data Control Language)
Grant, revoke.
4. TCL (Transaction Control Language)
Commit, rollback.
Advantages of SQL:-
1. SQL is non procedural programming language. It means in SQL, user will show that which data member is required not a accessing method to retrieve them.
2. SQL is very powerful language. It can perform all the task of DBMS like- data definition, data manipulation, data control and transaction control etc.
3. SQL is portable language. It means any application which supports RDBMS and can able to execute SQL query at any operating system, platform or computer RAM.
4. SQL is easily understandable and flexible language because it may be written in lower and upper case statements of English language. With it, we can write SQL query for query complex problem.
5. SQL includes DDL, DCL, DML commands which can executed on any type of RDBMS software like - Oracle, MySQL, DB2 etc.
6. SQL is high level language. SQL may be imbaded with any other programming language in form of script. SQL can work for any small or big personal or organisation's work.
7. SQL statements are applied on whole data cell so we can access result from large data base in minimum time.
8. In SQL to maintain data base security it will provide user name, password and previliges which can stop unauthorised access over data base a d maintain security for long time.
Disadvantages of SQL:-
1. SQL is non procedural programming language so we can perform any type of procedure, mapping conditions and checking in it.
2. It ha high transaction over head because we can execute a statement iteratively then in each iteration oracle engine demands some resources which will increase network traffic and we get slow response. This effect is show in multi user environment.
3. SQL doesn't provide facility for exception handling. It means if any SQL statement through an error during execution then it can not be controlled and SQL was displaying standard error message which is not user friendly.
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