SQL Q&A

What is SQL?

SQL is Structured Query Language, which is a computer language for storing, manipulating and retrieving data stored in relational database.

SQL is the standard language for Relation Database System. All relational database management systems like MySQL, MS Access, Oracle, Sybase, Informix, postgres and SQL Server use SQL as standard database language.

Also, they are using different dialects, such as:

• MS SQL Server using T-SQL,
• Oracle using PL/SQL,
• MS Access version of SQL is called JET SQL (native format), etc

Why SQL?

• Allows users to access data in relational database management systems.
• Allows users to describe the data.
• Allows users to define the data in database and manipulate that data.
• Allows to embed within other languages using SQL modules, libraries & pre-compilers.
• Allows users to create and drop databases and tables.
• Allows users to create view, stored procedure, functions in a database.
• Allows users to set permissions on tables, procedures, and views

Differences between SQL and PLSQL?

1.) SQL is a data oriented language for selecting and manipulating sets of data. PL/SQL is a procedural language to create applications.

2.) PL/SQL can be the application language just like Java or PHP can. PL/SQL might be the language we use to build, format and display those screens, web pages and reports.SQL may be the source of data for our screens, web pages and reports.

3.) SQL is executed one statement at a time. PL/SQL is executed as a block of code.

4.) SQL tells the database what to do (declarative), not how to do it. In contrast, PL/SQL tell the database how to do things (procedural).

5.) SQL is used to code queries, DML and DDL statements. PL/SQL is used to code program blocks, triggers, functions, procedures and packages.

6.) We can embed SQL in a PL/SQL program, but we cannot embed PL/SQL within a SQL statement.

What is RDBMS?

RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.

A Relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by E. F. Codd.

What is table ?

The data in RDBMS is stored in database objects called tables. The table is a collection of related data entries and it consists of columns and rows.

Remember, a table is the most common and simplest form of data storage in a relational database.

What is field?

Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.

A field is a column in a table that is designed to maintain specific information about every record in the table.

What is record or row?

A record, also called a row of data, is each individual entry that exists in a table. For example, there are 7 records in the above CUSTOMERS table.

A record is a horizontal entity in a table.

What is column?

A column is a vertical entity in a table that contains all information associated with a specific field in a table.

What is NULL value?

A NULL value in a table is a value in a field that appears to be blank which means A field with a NULL value is a field with no value.

It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation.