How Queries can be Categorized in Relational Database?

The queries to deal with relational database can be categorized as:

• Data Definition Language:It is used to define the structure of the database. e.g; CREATE TABLE, ADD COLUMN, DROP COLUMN and so on.
• Data Manipulation Language:It is used to manipulate data in the relations. e.g.; INSERT, DELETE, UPDATE and so on.
• Data Query Language:It is used to extract the data from the relations. e.g.; SELECT So first we will consider the Data Query Language. A generic query to retrieve data from a relational database is:

1. SELECT [DISTINCT] Attribute_List FROM R1,R2….RM
2. [WHERE condition]
3. [GROUP BY (Attributes)[HAVING condition]]
4. [ORDER BY(Attributes)[DESC]];

Part of the query represented by statement 1 is compulsory if you want to retrieve from a relational database. The statements written inside [] are optional. We will look at the possible query combination on relation shown in Table 1.

Structured Query Language is a standard Database language that is used to create, maintain, and retrieve the relational database. In this article, we will discuss this in detail about SQL. Following are some interesting facts about SQL. Let’s focus on that.

SQL is case insensitive. But it is a recommended practice to use keywords (like SELECT, UPDATE, CREATE, etc.) in capital letters and use user-defined things (like table name, column name, etc.) in small letters.

We can write comments in SQL using “–” (double hyphen) at the beginning of any line. SQL is the programming language for relational databases (explained below) like MySQL, Oracle, Sybase, SQL Server, Postgre, etc. Other non-relational databases (also called NoSQL) databases like MongoDB, DynamoDB, etc. do not use SQL.

Although there is an ISO standard for SQL, most of the implementations slightly vary in syntax. So we may encounter queries that work in SQL Server but do not work in MySQL.