Statistical Tests in AB Testing

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Overfitting vs Underfitting 🎯

Why do ML models fail? Usually because of one of these two villains:

Overfitting: The model memorizes training data but fails on new data. (Like a student who memorizes past exam questions but can’t handle a new one.)

Underfitting: The model is too simple to capture patterns. (Like using a straight line to fit a curve.)

The sweet spot? A model that generalizes well.

Note: Regularization, cross-validation, and more data usually help fight these problems.

Want to make a transition to a career in data?

Here is a 7-step plan for each data role

Data Scientist

Statistics and Math: Advanced statistics, linear algebra, calculus.
Machine Learning: Supervised and unsupervised learning algorithms.
xData Wrangling: Cleaning and transforming datasets.
Big Data: Hadoop, Spark, SQL/NoSQL databases.
Data Visualization: Matplotlib, Seaborn, D3.js.
Domain Knowledge: Industry-specific data science applications.

Data Analyst

Data Visualization: Tableau, Power BI, Excel for visualizations.
SQL: Querying and managing databases.
Statistics: Basic statistical analysis and probability.
Excel: Data manipulation and analysis.
Python/R: Programming for data analysis.
Data Cleaning: Techniques for data preprocessing.
Business Acumen: Understanding business context for insights.

Data Engineer

SQL/NoSQL Databases: MySQL, PostgreSQL, MongoDB, Cassandra.
ETL Tools: Apache NiFi, Talend, Informatica.
Big Data: Hadoop, Spark, Kafka.
Programming: Python, Java, Scala.
Data Warehousing: Redshift, BigQuery, Snowflake.
Cloud Platforms: AWS, GCP, Azure.
Data Modeling: Designing and implementing data models.

#data

Advanced SQL Optimization Tips for Data Analysts

1. Use Proper Indexing
Create indexes on frequently queried columns to speed up data retrieval.

2. Avoid `SELECT *`
Specify only the columns you need to reduce the amount of data processed.

3. Use `WHERE` Instead of `HAVING`
Filter your data as early as possible in the query to optimize performance.

4. Limit Joins
Try to keep joins to a minimum to reduce query complexity and processing time.

5. Apply `LIMIT` or `TOP`
Retrieve only the required rows to save on resources.

6. Optimize Joins
Use INNER JOIN instead of OUTER JOIN whenever possible.

7. Use Temporary Tables
Break large, complex queries into smaller parts using temporary tables.

8. Avoid Functions on Indexed Columns
Using functions on indexed columns often prevents the index from being used.

9. Use CTEs for Readability
Common Table Expressions help simplify nested queries and improve clarity.

10. Analyze Execution Plans
Leverage execution plans to identify bottlenecks and make targeted optimizations.

Happy querying!

SQL isn't easy!

It’s the powerful language that helps you manage and manipulate data in databases.

To truly master SQL, focus on these key areas:

0. Understanding the Basics: Get comfortable with SQL syntax, data types, and basic queries like SELECT, INSERT, UPDATE, and DELETE.


1. Mastering Data Retrieval: Learn advanced SELECT statements, including JOINs, GROUP BY, HAVING, and subqueries to retrieve complex datasets.


2. Working with Aggregation Functions: Use functions like COUNT(), SUM(), AVG(), MIN(), and MAX() to summarize and analyze data efficiently.


3. Optimizing Queries: Understand how to write efficient queries and use techniques like indexing and query execution plans for performance optimization.


4. Creating and Managing Databases: Master CREATE, ALTER, and DROP commands for building and maintaining database structures.


5. Understanding Constraints and Keys: Learn the importance of primary keys, foreign keys, unique constraints, and indexes for data integrity.


6. Advanced SQL Techniques: Dive into CASE statements, CTEs (Common Table Expressions), window functions, and stored procedures for more powerful querying.


7. Normalizing Data: Understand database normalization principles and how to design databases to avoid redundancy and ensure consistency.


8. Handling Transactions: Learn how to use BEGIN, COMMIT, and ROLLBACK to manage transactions and ensure data integrity.


9. Staying Updated with SQL Trends: The world of databases evolves—stay informed about new SQL functions, database management systems (DBMS), and best practices.

⏳ With practice, hands-on experience, and a thirst for learning, SQL will empower you to unlock the full potential of data!

You can read detailed article here

I've curated essential SQL Interview Resources👇
https://news.1rj.ru/str/DataSimplifier

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Hope it helps :)