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Learn SQL programming for Free-Beginner’s

SQL is the language behind an Application to perform operations like storing and retrieving data. It is a standard language for the relational database management system.

Do check our Programming Blog if you don’t covered it.

Here’s the Index 🙂

  1. What is SQL?
  2. Relational Database
  3. Database
  4. Relationships in SQL
  5. Conclusion
  6. FAQ

What is SQL?

learn sql

What is a Relational Database?

A relational database is a database that stores as well as retrieves data.

relational database

Basically the data is stored in systems is in the form of a table with n numbers of rows and columns. All relational database management systems like MySQL, MS Access, Oracle, PostgreSQL, etc use SQL as the standard database language.

SQL 

   SQL Commands

DDLDMLDCLTCLDCL
CREATEINSERTGRANTROLLBACKSELECT
ALTERUPDATEREVOKECOMMIT
TRUNCATEDELETESAVEPOINT
DROP
DESC
RENAME

What are DDL commands?(SQL)

DDL stands for Data Definition Language, used for definition and creation of objects in a table.

  1. CREATE 

Used to create tables, databases, etc.

  1. ALTER 

Used to modify the table.

  1. DROP

Used to remove a table.

  1. RENAME

Used to rename a table.

What are DML commands?(SQL)

DML stands for Data Manipulation Language, used for updates, retrieving data from a database.

  1. INSERT

Used to Insert data in a table.

  1. SELECT

Used to select a table’s data.

  1. UPDATE 

Used to update the table’s data.

  1. DELETE

Used to remove records from the table.

Database in SQL

SQL database

How to create a Database?

The CREATE DATABASE  statement is used to create a new database.

Syntax

CREATE DATABASE Database_name;

CREATE DATABASE is the keyword and the Database_Name is the name of the database that I am going to create.

Ex.

CREATE DATABASE MyRecords;

Note: All database names should be unique.

How to delete Databases?

To delete Databases we should use the drop keyword. 

Syntax

DROP DATABASE Database_Name;

Ex.

DROP DATABASE MyRecords;

Tables in SQL

Creating a Table

Customers

FieldTypeNullKey
IDintNOPRI
NAMEvarchar(20)NO
AGEintNO
ADDRESSchar(25)YES
SALARYfloatYES

The above table is the blueprint of the Customer table that we are going to create.

Let’s understand this.

In the field column, the following are the column’s head.

Type contains the data type of the columns.

Null is that column which shows that the section must contain a value or not.

Key, there are several types of keys, but we used the Primary key.

Primary Keys are the keys that are unique and also used to display details.

Let’s create a Table of Customers:

To create a table we have to use CREATE keyword

Syntax

CREATE TABLE table_name( column1 datatype, column2 datatype, column3 datatype ….. columnN datatype, PRIMARY KEY (one or more column’s name));

CREATE TABLE Customers(ID int PRIMARY KEY, NAME varchar(20), AGE int, ADDRESS char(25), SALARY float));

In the above line, we have created a Customers table.

To create should have columns names and their datatypes. As for the ID, it is an integer and also it is unique so we set it as our table’s primary key.

The primary key can’t be repeated.

SQL tables

We used varchar(20) and char(25) for Name and Address respectively because the Name and the address are Strings and for that, we used varchar and char with sizes.

The varchar is of variable length and the char is of fixed length.

Then we used salary, of datatype float which shows that the salary that is going to be entered is in the decimal value.

Rename a table

To rename, RENAME command is used.

Syntax

RENAME TABLE old_table_name to new_table_name;

Ex.

RENAME TABLE Customers to Customer;

Inserting Data into a table

To insert data we have to use the INSERT INTO keyword. Also, the values should be as per the data types.

Syntax

INSERT INTO Customer(ID, NAME,....);

Ex.

INSERT INTO Customer(1,’Ayush’,21, Panaji, Goa’,’2000.00’);

The String should be in single quotes( ‘ ‘ ) and there’s no need for integers.

If you want to skip a column then you just have to leave a space.

insert query in SQL

For ex.

If it’s an integer then you have to

 INSERT INTO Customer(1,’Ayush’, , Panaji, Goa’,’2000.00’);

You can see I skip the age. 

Not the ID because it’s a primary key and it should be filled and also be unique.

Displaying Table using SQL

To display a table we use the SELECT keyword. 

Syntax

SELECT * FROM TABLE_NAME;

Ex. 

SELECT * FROM Customer;

Here, the above query is going to return the Customer table with entries.

IDNAMEAGEADDRESSSALARY
1AYUSH18Panaji, Goa20000.00

This table is the result of the query.

Where * means to select all.

We can also display a single column

Ex. 

SELECT NAME FROM Customer;
NAME
AYUSH

This table is the result of the query.

Update SQL table

The above code is going to display only the Name column with its entries.

Also, we can search the table by

SELECT * FROM Customer WHERE NAME= AYUSH;
SELECT * FROM Customer WHERE AGE= 18;
SELECT * FROM Customer WHERE ID= 1;

In the first line of the above code, we request the entries of Ayush and * means all. So, the data I will get is the full row of all Ayush in the Name column.

IDNAMEAGEADDRESSSALARY
1AYUSH18Panaji, Goa20000.00

This table is the result of the query.

In the second query, I will get nothing because the Customer table doesn’t have any entry with age 18.

IDNAMEAGEADDRESSSALARY

This table is the result of the query.

In the third line, I will again get the full row of the 1 in ID.

IDNAMEAGEADDRESSSALARY
1AYUSH18Panaji, Goa20000.00

This table is the result of the query.

Updating 

The UPDATE keyword is used to modify the existing rows in a table.

Syntax

UPDATE TABLE_NAME SET column1 = value1, column2 = value2, … … … valueN WHERE [condition];

Ex.

UPDATE Customer SET ADDRESS = ‘PUNE’ WHERE ID =1;
IDNAMEAGEADDRESSSALARY
1AYUSH18PUNE20000.00

This table is the result of the query.

DELETE

To remove an entry from the table we can use the DELETE keyword.

Syntax

DELETE FROM table_name WHERE[condition];

Ex.

DELETE FROM Customer WHERE ID=1;
IDNAMEAGEADDRESSSALARY

Empty. This table is the result of the query.

Relationships in SQL

Relationships in DBMS can be stated as a relation between two entities like College-Department, Student-Course, etc.

There are 3 types of Relationship.

1 : 1 ( One to One) Relationship.

The one to one relationship is the relationship in which the instance of the tables is associated with each other.

Ex. Let’s take an example of a student table and standard table.

Student Table

Student_IDStudent Name
1Ayush
2Ramesh

Course Tabe

Course_IDCourse_Name
1Science
2Commerce

If I want to attach both tables then I should make a foreign key on a table which is the primary key of another

Ex.

CREATE TABLE Student(Student_ID int PRIMARY KEY, Student_Name varchar(20), Course_ID int REFERENCES COURSE(Course_ID));

We used the Course_ID as a foreign key in the Student table. The references is a keyword to associate the table, also we have to mention table_name(table_id_primary_key)

Student table

Student_IDStudent_NameCourse_ID
1Ayush1
2Ramesh2

In 1:1, we should use any table.

You can see that I made a new column of Course_ID which is the primary key of course.

If you run the query

SELECT * FROM Student WHERE Course_name=Science.

You will get this result

Student_IDStudent_NameCourse_ID
1Ayush1

1 : M or M : 1 ( One to Many or Many to One ) Relationship.

One to Many or the Many to One relationship used for that table whose columns are more,or that which depends on another table.

Let’s take two tables Student and Marks.

As you know, the Marks table is going to depend on the Student table. So, we are going to move the primary key of Marks to the Student table as a foreign key.

CREATE TABLE Student(Student_ID int PRIMARY KEY, Student_Name varchar(20), Marks_ID int REFERENCES Marks(Marks_ID));

Student table

Student_IDStudent_NameMarks_ID
1Ayush1
2Ramesh2

Marks Table

Marks_IDSubjectMarks
1Bio85
2Maths60

If you run the query

SELECT * FROM Student WHERE Marks=60

You will get this result

Student_IDStudent_NameMarks_IDSubjectMarks
2Ramesh2Maths60

M : M ( Many to Many ) Relationship.  

When there are two tables and both depend on each other, you can make a third table to join these two.

 Ex. If two tables Student and teachers have columns like name, id, subject etc, then we will have to create a third table with both tables’s primary key as foreign keys.

Student

Student_IDStudent_NameSubjectMarks
1AyushBio85
2RameshMaths60

Teacher

Teacher_IDTeacher_NameSubject
1Miss NehaMaths
2Mr. PandeyBio

To connect these tables we have to create another table.

CREATE TABLE Stud_Teach(Student_ID int REFERENCES Students(Student_ID) ,Teacher_ID int REFERENCES Teacher(Teacher_ID));
Student_IDTeacher_ID
12
21

Conclusion

The SQL is easy. But the relationship is a bit hard to learn and to understand where to apply.

So, read books and tutorials and be perfect, because it is easy and if you master any development programming language, then you will need the Database to store its files.

So, there we use SQL queries.

FAQ

Q1. What is full-form of SQL?

Structured Query Language.

Q2. How I download SQL

There are various SQL software. I prefer MySQL.

Q3. Why SQL is required?

To store Information on server and to access that information from anywhere.

Q4. Is SQL easy?

Yes, there’s no need of coding.

Q5. Any compulsion of learning SQL for a programmer?

No, until you opt for Full stack development.

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