SQL Quick Notes to refresh your concepts

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The SQL EXISTS operator tests the existence of any value in a subquery i.e. it executes the outer SQL query only if the subquery is not NULL (empty result-set),making it perfect for validating the presence of related data.

The result of EXISTS is a boolean value either True or False

We can also use the NOT operator to inverse the working of the EXISTS clause. The SQL command executes if the subquery returns an empty result-set.

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🔅 Most important SQL commands

Frequently asked SQL interview questions for Data Analyst/Data Engineer role-

1 - What is SQL and what are its main features?
2 - Order of writing SQL query?
3- Order of execution of SQL query?
4- What are some of the most common SQL commands?
5- What’s a primary key & foreign key?
6 - All types of joins and questions on their outputs?
7 - Explain all window functions and difference between them?
8 - What is stored procedure?
9 - Difference between stored procedure & Functions in SQL?
10 - What is trigger in SQL?
11 - Difference between where and having?

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Do not wait till you've mastered SQL till you apply to your first Data Analyst Job.

You can do both at the same time.

📊Here's a breakdown of SQL interview questions covering various topics:

🔺Basic SQL Concepts:
-Differentiate between SQL and NoSQL databases.
-List common data types in SQL.

🔺Querying:
-Retrieve all records from a table named "Customers."
-Contrast SELECT and SELECT DISTINCT.
-Explain the purpose of the WHERE clause.


🔺Joins:
-Describe types of joins (INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL JOIN).
-Retrieve data from two tables using INNER JOIN.

🔺Aggregate Functions:
-Define aggregate functions and name a few.
-Calculate average, sum, and count of a column in SQL.

🔺Grouping and Filtering:
-Explain the GROUP BY clause and its use.
-Filter SQL query results using the HAVING clause.

🔺Subqueries:
-Define a subquery and provide an example.

🔺Indexes and Optimization:
-Discuss the importance of indexes in a database.
&Optimize a slow-running SQL query.

🔺Normalization and Data Integrity:
-Define database normalization and its significance.
-Enforce data integrity in a SQL database.

🔺Transactions:
-Define a SQL transaction and its purpose.
-Explain ACID properties in database transactions.

🔺Views and Stored Procedures:
-Define a database view and its use.
-Distinguish a stored procedure from a regular SQL query.

🔺Advanced SQL:
-Write a recursive SQL query and explain its use.
-Explain window functions in SQL.

✅👀These questions offer a comprehensive assessment of SQL knowledge, ranging from basics to advanced concepts.

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SQL Interview Ques & ANS 💥👇
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Here you can find the detailed answers for the above questions
👇👇
https://medium.com/@data_analyst/top-25-sql-questions-to-crack-your-next-data-analytics-interview-de6ab3634e1e

Frequently asked SQL interview questions for Data Analyst/Data Engineer role-

1 - What is SQL and what are its main features?
2 - Order of writing SQL query?
3- Order of execution of SQL query?
4- What are some of the most common SQL commands?
5- What’s a primary key & foreign key?
6 - All types of joins and questions on their outputs?
7 - Explain all window functions and difference between them?
8 - What is stored procedure?
9 - Difference between stored procedure & Functions in SQL?
10 - What is trigger in SQL?
11 - Difference between where and having?

❌Common Mistakes In SQL JOINS

Interviewer can only trick you with two things in SQL JOIN questions!🤷

Maximum people are making the most common mistake in SQL JOIN even after gaining few years of experience!

What makes SQL JOIN tricky?
1. Duplicate Values
2. NULL

Once you understand handling both, you can solve any of the toughest SQL JOIN questions in any interview.

Read more.....