Learn SQL Queries Part1

 

SQL Queries using MySQL Database Part-1

Part-2

Understanding an RDBMS Relational Database Management System(RDBMs), stores all information/data  in the form of Tables. 

Understanding a Relational Database
A single database can contain many tables, and they can be linked together.
When the tables are linked together, it's said to be a relational database.

 

Understanding Tables, Records and Fields in RDBMS

Table: Collection of rows and columns
Row:  Collection of inter related columns.
Field:  A piece of information of particular entity.

 

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Table structure/design: 

example:

FieldName             Datatype
Id                            Number
First_Name            Text
Last_Name            Text
Address                 Text

Understanding Primary and Foreign Keys
 

Primary key:Identifies each record in table with unique id.

example:

• account_no
• roll_no
• customer_no
• emp_no..etc
  

Foriegnkey:

A foreign key is a field (or fields) that points to the primary key of another table.
A foreign key is a column, or combination of columns, that contain values that are found in the primary key of some table.
 

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Understanding SQL and SQL Queries

 

SQL(Structured Query Language): 

Used to interact with the Databases. There are plenty of SQL Queries that are used to query the data. Basically, they are categorized into 3 groups.

1. DDL
2. DML
3. DCL
   

1. DDL(Data Definition Language): All the commands in this category are used on table definition(design/structure) such as creating , changing field name, datatype, size, add or remove fields etc, you can also find commands for creating, altering or deleting any database objects such as user,view etc.

•  Create
•  Alter
•  Drop  

2. DML(Data Manipulation Language): These are commands used on table data.

•  Select
•  Insert
•  Update
•  Delete

3. DCL(Data Control Language):These command are used for securing data.

• Grant
• Revoke

In the next blog, we will discuss in detail on the above stated commands. Please follow the Link given below.