SQL Notes

Hub Advantages and Disadvantages of SQL Features of SQL History of SQL SQL vs NoSQL What is SQL?SQL Comments SQL Data Types SQL Keywords SQL Operators SQL Syntax CHECK Constraint in SQL Composite Keys in SQL DEFAULT Constraint in SQL FOREIGN KEY Constraint in SQL NOT NULL Constraint in SQL PRIMARY KEY Constraint in SQL SQL Constraints UNIQUE Key Constraint in SQL DELETE Data INSERT Data SELECT Data SQL Aliases UPDATE Data BETWEEN Operator DISTINCT Keyword GROUP BY Clause HAVING Clause IN Operator LIKE Operator LIMIT Clause ORDER BY Clause TOP Clause WHERE Clause Wildcard Characters EXCEPT Operator in SQL INTERSECT Operator in SQL MINUS Operator in SQL UNION Operator in SQL UNION ALL Operator in SQL CROSS JOIN in SQL FULL OUTER JOIN INNER JOIN JOIN vs UNION LEFT JOIN RIGHT JOIN SELF JOIN SQL Joins Overview ANY and ALL Operators CASE Expression in SQL Correlated Subquery EXISTS Operator Nested Subqueries in SQL Scalar Subqueries Subquery Introduction Aggregate Functions AVG Function Conversion Functions COUNT Function Date Functions MIN and MAX Functions Numeric Functions String Functions SUM Function ALTER TABLE Create Table DROP TABLE Rename Table Temporary Table TRUNCATE TABLE Backup Database Create Database Drop Database Restore Database CREATE VIEW in SQL DROP VIEW in SQL Materialized Views in SQL Update and Modify Views in SQL Create Stored Procedure in SQL Execute Stored Procedures in SQL Parameters in Stored Procedures Stored Procedure vs Function in SQL Stored Procedure Introduction AFTER Trigger BEFORE Trigger INSTEAD OF Trigger Trigger Examples Trigger Introduction ACID Properties in SQL COMMIT in SQL Isolation Levels in SQL ROLLBACK in SQL SAVEPOINT in SQL Introduction to SQL Transactions Boyce-Codd Normal Form (BCNF)Database Normalization Denormalization First Normal Form (1NF)Second Normal Form (2NF)Third Normal Form (3NF)Clustered Index in SQL Index Performance Non-Clustered Index Introduction to SQL Indexes Unique Index SQL Execution Plans EXPLAIN Plan Indexing Strategies Partitioning Query Optimization SQL Performance Tips Common Table Expressions (CTE)Dynamic SQL Functions in SQL Materialized Views MERGE Statement PIVOT and UNPIVOT RANK(), DENSE_RANK(), and ROW_NUMBER()Recursive CTE Stored Procedures Triggers in SQL Views in SQL Window Functions SQL Challenges SQL Exercises (Advanced)SQL Exercises (Beginner)SQL Exercises (Intermediate)SQL Projects SQL Interview Questions (Advanced)SQL Interview Questions (Beginner)SQL Interview Questions (Intermediate)SQL Output-Based Interview Questions SQL Scenario-Based Interview Questions Create Your First Database Install MySQL on Your Computer Install PostgreSQL Install SQLite SQL Online Compilers SQL Roadmap

SQL Interview Questions (Beginner)

Learn the most important beginner-level SQL interview questions with answers, examples, and explanations commonly asked in technical interviews.

Great work!

You've made it through:

text example

SQL Basics
SQL Intermediate
SQL Advanced
SQL Optimization

Now comes the fun part:

text example

Interviews
Technical Tests
Viva Exams
Campus Placements

This section has the interview questions you'll actually see.

These questions work for:

text example

Freshers
Students
Internship Interviews
Junior Developers
Campus Placements

Q1. What is SQL?

Answer

SQL is short for:

text example

Structured Query Language

It's what you use to:

text example

Store Data
Retrieve Data
Update Data
Delete Data
Manage Databases

Example

sql example

SELECT *
FROM Employees;

Q2. What are the main categories of SQL commands?

Answer

SQL commands break down into five types:

Output

DDL
DML
DQL
DCL
TCL

DDL

Deals with structure:

text example

CREATE
ALTER
DROP
TRUNCATE

DML

Deals with data:

text example

INSERT
UPDATE
DELETE

DQL

Gets data:

text example

SELECT

DCL

Controls access:

text example

GRANT
REVOKE

TCL

Manages transactions:

text example

COMMIT
ROLLBACK
SAVEPOINT

Q3. What is a Database?

Answer

A database is just structured data that you can easily store, manage, and pull from whenever you need it.

Example

text example

Student Database
Bank Database
Hospital Database

Q4. What is a Table?

Answer

A table is how data gets organized — rows and columns, like a spreadsheet.

Example

EmployeeID	EmployeeName
1	Rahul
2	Priya

Q5. What is a Row?

Answer

A row is one complete record.

Example:

text example

1 Rahul

That's one row.

Q6. What is a Column?

Answer

A column is a single piece of information across all records.

Example:

text example

EmployeeID
EmployeeName
Salary

Q7. What is a Primary Key?

Answer

A primary key uniquely identifies each record — no two rows can have the same primary key.

What you need to know:

text example

Unique
Cannot Be NULL
One Primary Key Per Table

Example:

sql example

EmployeeID INT PRIMARY KEY

Q8. What is a Foreign Key?

Answer

A foreign key connects two tables by referencing another table's primary key.

Example:

sql example

DepartmentID INT,

FOREIGN KEY
(
    DepartmentID
)

REFERENCES Departments
(
    DepartmentID
)

Q9. Difference Between Primary Key and Foreign Key?

Feature	Primary Key	Foreign Key
Uniqueness	Yes	No
NULL Allowed	No	Yes
Purpose	Identify Row	Create Relationship

Q10. What is a Constraint?

Answer

Constraints are rules you put on columns to keep data clean and reliable.

Examples:

Output

PRIMARY KEY
FOREIGN KEY
UNIQUE
CHECK
DEFAULT
NOT NULL

Q11. What is NOT NULL Constraint?

Answer

This says "you must have a value here" — no blanks allowed.

Example:

sql example

Name VARCHAR(100)
NOT NULL

Q12. What is UNIQUE Constraint?

Answer

Every value in this column has to be different from every other value.

Example:

sql example

Email VARCHAR(100)
UNIQUE

Q13. What is the Difference Between DELETE, TRUNCATE, and DROP?

Feature	DELETE	TRUNCATE	DROP
Removes Rows	Yes	Yes	Yes
Removes Table	No	No	Yes
WHERE Allowed	Yes	No	No
Rollback Possible	Yes*	Depends	No

Q14. What is the Difference Between CHAR and VARCHAR?

CHAR

Fixed width — if you say CHAR(10) and input 5 characters, it pads with spaces.

Example:

sql example

CHAR(10)

VARCHAR

Variable width — only takes the space it needs.

Example:

sql example

VARCHAR(10)

Q15. What is NULL?

Answer

NULL means "I don't have a value for this" — missing data.

Example:

Output

Phone Number Not Provided

Q16. What is the Difference Between NULL and 0?

NULL

Unknown value. We don't know what it is.

0

Actual number. You know it's zero.

Q17. What is SQL JOIN?

Answer

JOIN pulls data from multiple tables by matching rows on a shared column.

Example:

sql example

SELECT *

FROM Employees E

JOIN Departments D

ON E.DepartmentID =
   D.DepartmentID;

Q18. What are Different Types of JOINs?

Your main options:

Output

INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL JOIN
SELF JOIN
CROSS JOIN

Q19. What is INNER JOIN?

Answer

Returns only the rows where there's a match in both tables.

Example:

sql example

SELECT *

FROM Employees E

INNER JOIN Departments D

ON E.DepartmentID =
   D.DepartmentID;

Q20. What is LEFT JOIN?

Answer

Returns everything from the left table, plus matching rows from the right table. If there's no match, you still get the left table data.

Q21. What is RIGHT JOIN?

Answer

Same as LEFT JOIN, but the other way around — everything from the right table plus matches.

Q22. What is FULL OUTER JOIN?

Answer

Returns all rows from both tables. If something matches, great. If not, you still get it.

Q23. What is a Subquery?

Answer

A query inside another query. Useful when you need results from one query to filter another.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for SQL Interview Questions (Beginner).

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this SQL Complete Guide topic.

Search Terms

sql-complete-guide, sql complete guide, sql, complete, guide, interview, questions, beginner

Continue learning this concept

Interview QuestionsSQL Interview Questions (Advanced)Learn advanced SQL interview questions with detailed answers covering query optimization, execution plans, indexing, partitioning, transactions, window functions, and database architecture.Interview QuestionsSQL Interview Questions (Intermediate)Learn the most important intermediate-level SQL interview questions with detailed answers, examples, joins, subqueries, indexing, transactions, and optimization concepts.Interview QuestionsSQL Output-Based Interview QuestionsLearn the most important SQL output-based interview questions with tables, queries, outputs, explanations, and interview tips.Interview QuestionsSQL Scenario-Based Interview QuestionsLearn the most important SQL scenario-based interview questions with practical solutions, query logic, optimization techniques, and real-world database cases.Advanced SQLTriggers in SQLLearn SQL Triggers in detail, understand automatic database actions, BEFORE and AFTER triggers, event-driven execution, auditing, validation, and real-world applications.PracticeSQL Exercises (Beginner)Practice beginner-level SQL exercises covering SELECT, WHERE, ORDER BY, GROUP BY, JOINs, aggregate functions, and basic database operations.

PreviousSQL Interview Questions (Advanced)NextSQL Interview Questions (Intermediate)

SQL Notes

SQL Interview Questions (Beginner)

Learn the most important beginner-level SQL interview questions with answers, examples, and explanations commonly asked in technical interviews.

Great work!

You've made it through:

text example

SQL Basics
SQL Intermediate
SQL Advanced
SQL Optimization

Now comes the fun part:

text example

Interviews
Technical Tests
Viva Exams
Campus Placements

This section has the interview questions you'll actually see.

These questions work for:

text example

Freshers
Students
Internship Interviews
Junior Developers
Campus Placements

Q1. What is SQL?

Answer

SQL is short for:

text example

Structured Query Language

It's what you use to:

text example

Store Data
Retrieve Data
Update Data
Delete Data
Manage Databases

Example

sql example

SELECT *
FROM Employees;

Q2. What are the main categories of SQL commands?

Answer

SQL commands break down into five types:

Output

DDL
DML
DQL
DCL
TCL

DDL

Deals with structure:

text example

CREATE
ALTER
DROP
TRUNCATE

DML

Deals with data:

text example

INSERT
UPDATE
DELETE

DQL

Gets data:

text example

SELECT

DCL

Controls access:

text example

GRANT
REVOKE

TCL

Manages transactions:

text example

COMMIT
ROLLBACK
SAVEPOINT

Q3. What is a Database?

Answer

A database is just structured data that you can easily store, manage, and pull from whenever you need it.

Example

text example

Student Database
Bank Database
Hospital Database

Q4. What is a Table?

Answer

A table is how data gets organized — rows and columns, like a spreadsheet.

Example

EmployeeID	EmployeeName
1	Rahul
2	Priya

Q5. What is a Row?

Answer

A row is one complete record.

Example:

text example

1 Rahul

That's one row.

Q6. What is a Column?

Answer

A column is a single piece of information across all records.

Example:

text example

EmployeeID
EmployeeName
Salary

Q7. What is a Primary Key?

Answer

A primary key uniquely identifies each record — no two rows can have the same primary key.

What you need to know:

text example

Unique
Cannot Be NULL
One Primary Key Per Table

Example:

sql example

EmployeeID INT PRIMARY KEY

Q8. What is a Foreign Key?

Answer

A foreign key connects two tables by referencing another table's primary key.

Example:

sql example

DepartmentID INT,

FOREIGN KEY
(
    DepartmentID
)

REFERENCES Departments
(
    DepartmentID
)

Q9. Difference Between Primary Key and Foreign Key?

Feature	Primary Key	Foreign Key
Uniqueness	Yes	No
NULL Allowed	No	Yes
Purpose	Identify Row	Create Relationship

Q10. What is a Constraint?

Answer

Constraints are rules you put on columns to keep data clean and reliable.

Examples:

Output

PRIMARY KEY
FOREIGN KEY
UNIQUE
CHECK
DEFAULT
NOT NULL

Q11. What is NOT NULL Constraint?

Answer

This says "you must have a value here" — no blanks allowed.

Example:

sql example

Name VARCHAR(100)
NOT NULL

Q12. What is UNIQUE Constraint?

Answer

Every value in this column has to be different from every other value.

Example:

sql example

Email VARCHAR(100)
UNIQUE

Q13. What is the Difference Between DELETE, TRUNCATE, and DROP?

Feature	DELETE	TRUNCATE	DROP
Removes Rows	Yes	Yes	Yes
Removes Table	No	No	Yes
WHERE Allowed	Yes	No	No
Rollback Possible	Yes*	Depends	No

Q14. What is the Difference Between CHAR and VARCHAR?

CHAR

Fixed width — if you say CHAR(10) and input 5 characters, it pads with spaces.

Example:

sql example

CHAR(10)

VARCHAR

Variable width — only takes the space it needs.

Example:

sql example

VARCHAR(10)

Q15. What is NULL?

Answer

NULL means "I don't have a value for this" — missing data.

Example:

Output

Phone Number Not Provided

Q16. What is the Difference Between NULL and 0?

NULL

Unknown value. We don't know what it is.

0

Actual number. You know it's zero.

Q17. What is SQL JOIN?

Answer

JOIN pulls data from multiple tables by matching rows on a shared column.

Example:

sql example

SELECT *

FROM Employees E

JOIN Departments D

ON E.DepartmentID =
   D.DepartmentID;

Q18. What are Different Types of JOINs?

Your main options:

Output

INNER JOIN
LEFT JOIN
RIGHT JOIN
FULL JOIN
SELF JOIN
CROSS JOIN

Q19. What is INNER JOIN?

Answer

Returns only the rows where there's a match in both tables.

Example:

sql example

SELECT *

FROM Employees E

INNER JOIN Departments D

ON E.DepartmentID =
   D.DepartmentID;

Q20. What is LEFT JOIN?

Answer

Returns everything from the left table, plus matching rows from the right table. If there's no match, you still get the left table data.

Q21. What is RIGHT JOIN?

Answer

Same as LEFT JOIN, but the other way around — everything from the right table plus matches.

Q22. What is FULL OUTER JOIN?

Answer

Returns all rows from both tables. If something matches, great. If not, you still get it.

Q23. What is a Subquery?

Answer

A query inside another query. Useful when you need results from one query to filter another.

Exam Focus

Revise definitions, diagrams, examples, and short-answer points for SQL Interview Questions (Beginner).

Interview Use

Prepare one clear explanation, one practical example, and one common mistake for this SQL Complete Guide topic.

Search Terms

sql-complete-guide, sql complete guide, sql, complete, guide, interview, questions, beginner

Continue learning this concept

PreviousSQL Interview Questions (Advanced)NextSQL Interview Questions (Intermediate)