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75+ SQL Interview Questions

⇩

 Level: Beginner to Medium
Topics:

➊ Introduction to RDBMS
➋ Normalisation
➌ Introduction to SQL
➍ Tables and Fields
➎ Constraints
➏ DDL
➐ DML & DQL
➑ Joins
➊ Introduction to RDBMS

➀ What is a Database?
➁ What are different types of Databases?
➂ What is DBMS?
➃ What is difference between Database and DBMS?
➄ What is RDBMS?
➅ Which are popular RDBMS vendors?
➆ What is ACID property in Database?
➋ Normalisation

➀ What is Normalisation?
➁ Why is Normalisation necessary?
➂ What are the disadvantages of not performing Normalisation?
➃ What are different Normal Forms (NF)?
➄ What is Denormalisation?
➌ Introduction to SQL

➀ What is SQL?
➁ What is the use of SQL?
➂ Is SQL a programming language?
➃ What are the different parts of SQL?
Or,
➄ Group SQL commands in different parts.
➅ What is DDL?
➆ What is DML?
➇ What is DQL?
➈ What is DCL?
➉ What is TCL?
➍ Tables and Fields

➀ What is a Table?
➁ What is a field in a Table?
➂ Write a SQL command to create a Table.
➃ How to change the name of a Table?
➄ How to truncate a table?
➅ How to drop a table?
➎ Constraints

➀ What is a constraint?
➁ What are different levels of constraints?
➂ Give examples of various constraints?
➃ What is a primary key?
➄ What is a unique key?
➅ Difference between a primary key and a unique key.
➆ What is a foreign key?
➇ What is NULL value?
➈ What is NOT NULL constraint?
➉ Is blank space or Zero (0) same as NULL?
➏ DDL

➀ Give some examples of DDL commands
➁ Write the syntax of creating a table
➂ How to specify the default value for a column?
➃ How to specify a foreign key?
➄ How to specify a unique key?
➅ How to specify multiple columns as the primary key?
➆ What are different constraints you can add to a column while creating a table?
➇ How to create a copy of a table? (both structure and, data)
➈ You have 'n' tables and asked to create a separate table which will contain a few columns from these tables with data being copied.
➉ What is SELECT INTO used for? (In SQL Server)
➀➀ Difference between ALTER and RENAME
➀➁ Can a previously nullable column be altered to a NOT NULL column? If yes, explain the steps.
➐ DML & DQL

➀ How to insert rows into a table?
➁ What are different syntaxes for inserting records into a table?
➂ What is the syntax to insert multiple records at a time?
➃ How to update data in a table?
➄ How to delete a row in a table?
➅ Difference between DELETE and TRUNCATE?
➆ Explain how DML operations are performed on a View.
Or,
➇ Are Views used only for SELECT queries?
➈ How to fetch rows of a table?
➉ What is a query condition? How to write it in SQL?
➀➀ How to sort the fetched records?
➀➁ What is grouping? How to write in SQL?
➀➂ How to find how many records are being fetched?
➀➃ How to find the maximum and minimum value for a field in fetched records?
➀➄ How to sum values in a field for all records?
➑ Joins

➀ What is a join in SQL?
➁ What are the different types of joins?
➂ What is Inner Join?
➃ What is Left Outer Join?
➄ What is Right Outer Join?
➅ What is Full Outer Join?
➆ What is Cross Join?
➇ What is a Self Join?
➈ What is Equi Join?
➉ What is Natural Join?

➀➀ Given a query in Cross Join, convert it into an Inner Join.

➀➁ Given a query in Right Outer Join, convert it into a Left Outer Join.
➀➂ Convert an Inner Join into an Equi Join.
Or,
➀➃ What is required to convert an Inner Join into an Equi Join?

➀➄ What should be taken care of to improve the performance of queries containing Joins.
🚥 Disclaimer

⬘ The questions covered here are mostly conceptual

⬗ I never claim only these types of questions are/should be asked during interviews

⬙ For interviews, you should have fundamentals strong. And you should be able to provide solutions to practical problems.
Hey 👋

I am a Tech Educator and, Mentor from India 🇮🇳

I am sharing Tutorials, Tips, Techniques, Infographics, Cheat Sheets, Practice Questions, Project Ideas and Roadmaps on Web Development, DSA and, Databases.

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👩‍💻 Beginning Words

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❍ PL/SQL
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➤ SQL Tutorial for

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HTML & CSS → 👩‍💻 → JavaScript → 👩‍💻
↓
👩‍💻 ← React* ← 👩‍💻 ← Tailwind*
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👩‍💻 75+ SQL Practice Questions

❍ Oracle
❍ MySQL
❍ SQL Server
❍ PostgreSQL
❍ SQLite

⇩

Topics covered:

➊ Table
➋ Constraints
➀ Primary Key
➁ Unique
➂ Not Null
➃ Default
➄ Check
➅ Foreign Key
➌ Insert, Update, Delete
➍ Select

➊ Table

➀ Create a Table with a few fields by specifying their data types.

➁ Add a field to an existing table.

➂ Modify a field's data type of a table.

➃ Rename a field's name.

➄ Remove a field from a table.

➅ Rename a table's name.

➆ Drop a table.

➋ Constraints

➀ Primary Key
➁ Unique
➂ Not Null
➃ Default
➄ Check
➅ Foreign Key

➋.➀ Primary Key

➤ Create a Table with
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➁ 2 or, more fields as the primary key
...

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💎 Direct Link for High-Resolution Image

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➀ all
➁ background
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➃ font
➄ text-align
➅ text-decoration
➆ text-emphasis
➇ list-style
➈ offset
➉ overflow

➀➀ inset
➀➁ inset-block
➀➂ inset-inline
➀➃ margin
➀➄ margin-block
➀➅ margin-inline
➀➆ padding
➀➇ padding-block
➀➈ padding-inline
20. overscroll-behavior
➁➀ scroll-margin
➁➁ scroll-padding

➁➂ border
➁➃ border-top
➁➄ border-right
➁➅ border-bottom
➁➆ border-left
➁➇ border-block
➁➈ border-block-start
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➂➁ border-inline-start
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தொல்லை இரும்பிறவிச் சூழும் தளை நீக்கி
அல்லல் அறுத்து ஆனந்தம் ஆக்கியதே – எல்லை
மருவா நெறியளிக்கும் வாதவூர் எங்கோன்
திருவாசகம் என்னும் தேன்

பொருள்:
1.எப்போது ஆரம்பித்தது என அறியப்படமுடியாத தொலை காலமாக (தொல்லை)

2. இருந்து வரும் (இரும்)


3.பிறவிப் பயணத்திலே ஆழ்த்துகின்ற (பிறவி சூழும்)

4.அறியாமையாகிய இடரை (தளை)

5.அகற்றி (நீக்கி),

6.அதன் விளைவால் சுகதுக்கமெனும் துயரங்கள் விலக (அல்லல் அறுத்து),

7.முழுநிறைவாய்த் தன்னுளே இறைவனை உணர்த்துவதே (ஆனந்த மாக்கியதே),

8.பிறந்து இறக்கும் காலவெளிகளில் (எல்லை)

9.பிணைக்காமல் (மருவா)

10.காக்கும் மெய்யறிவினைத் தருகின்ற (நெறியளிக்கும்),

11.என் தலைவனான மாணிக்க வாசகரின் (வாதவூரெங்கோன்)

12.திருவாசகம் எனும் தேன் (திருவா சகமென்னுந் தேன்)

முதல்வரி: பிறவி என்பது முன்வினை விதையால் முளைப்பதோர் பெருமரம். அந்த ‘முன்வினை’ எங்கு ஆரம்பித்தது எனச் சொல்ல இயலாது. ஆனால் ‘அறியாமை’ ஒன்றே ஆசைக்கும்,, அச்சத்துக்கும் காரணம் என்பதால், அவையே வினைகளை விளைவிப்பன என்பதால், தொடர்ந்து வரும் பிறவிகளுக்கு, ‘அறியாமையே’ காரணம்

அறியாமைக்கு ஆரம்பம் கிடையாது. நமக்கு ஒரு பொருளைப் பற்றிய அறிவு எப்போதிருந்து இல்லை? அதைச் சொல்ல முடியாது. அதனாலேதான் முதலடியில், ஆரம்பமில்லாத அஞ்ஞானத்தை பிறவிகளுக்குக் காரணமாகச் சொல்லியது. ஆனால் அறியாமை, அறிவின் எழுச்சியால், அப்போதே முடிந்து விடும்.
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As champaka flowers are offered to Sri Vishnu here, it is called Champakadhama.


It is believed that King Janmejaya had sarpa-dosha. To get rid of it, he took bath in the nearby pond. He emerged with a golden body and sarpa-dosha was also removed. The pond is called Swarnamukhi and believed to have curative powers.
Sri Vishnu murti was consecrated by him.


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हिमालय पर्वत की एक बड़ी पवित्र गुफा थी।उस गुफा के निकट ही गंगा जी बहती थी।एक बार देवर्षि नारद विचरण करते हुए वहां आ पहुंचे।वह परम पवित्र गुफा नारद जी को अत्यंत सुहावनी लगी।वहां का मनोरम प्राकृतिक दृश्य,पर्वत,नदी और वन देख उनके हृदय में श्रीहरि विष्णु की भक्ति अत्यंत बलवती हो उठी।


और देवर्षि नारद वहीं बैठकर तपस्या में लीन हो गए।इन्द्र नारद की तपस्या से घबरा गए।उन्हें हमेशा की तरह अपना सिंहासन व स्वर्ग खोने का डर सताने लगा।इसलिए इन्द्र ने नारद की तपस्या भंग करने के लिए कामदेव को उनके पास भेज दिया।वहां पहुंच कामदेव ने अपनी माया से वसंतऋतु को उत्पन्न कर दिया।


पेड़ और पौधों पर रंग बिरंगे फूल खिल गए और कोयलें कूकने लगी,पक्षी चहकने लगे।शीतल,मंद,सुगंधित और सुहावनी हवा चलने लगी।रंभा आदि अप्सराएं नाचने लगीं ।किन्तु कामदेव की किसी भी माया का नारद पे कोई प्रभाव नहीं पड़ा।तब कामदेव को डर सताने लगा कि कहीं नारद क्रोध में आकर मुझे श्राप न देदें।

जैसे ही नारद ने अपनी आंखें खोली, उसी क्षण कामदेव ने उनसे क्षमा मांगी।नारद मुनि को तनिक भी क्रोध नहीं आया और उन्होने शीघ्र ही कामदेव को क्षमा कर दिया।कामदेव प्रसन्न होकर वहां से चले गए।कामदेव के चले जाने पर देवर्षि के मन में अहंकार आ गया कि मैने कामदेव को हरा दिया।

नारद फिर कैलाश जा पहुंचे और शिवजी को अपनी विजयगाथा सुनाई।शिव समझ गए कि नारद अहंकारी हो गए हैं और अगर ये बात विष्णु जी जान गए तो नारद के लिए अच्छा नहीं होगा।ये सोचकर शिवजी ने नारद को भगवन विष्णु को ये बात बताने के लीए मना किया। परंतु नारद जी को ये बात उचित नहीं लगी।
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