
Kosmas Botsis
Verified Expert in Engineering
Data Engineer and Developer
Athens, Central Athens, Greece
Toptal member since July 18, 2025
Kosmas is a results-driven full-stack data engineer and analyst with over 10 years of experience turning raw data into actionable insights. He has extensive experience building scalable, efficient data processes. Kosmas specializes in end-to-end data solutions, including data ingestion, transformation, modeling, and visualization.
Portfolio
Experience
- SQL - 15 years
- PostgreSQL - 10 years
- Data Engineering - 10 years
- Data Analytics - 10 years
- Looker Studio - 8 years
- BigQuery - 8 years
- Looker - 5 years
- dbt Cloud - 4 years
Preferred Environment
Windows, Slack, Teams, Google, Visual Studio Code (VS Code), Jira, Notion, Google Meet, Zoom, Data Build Tool (dbt), Looker, BigQuery
The most amazing...
...enterprise data systems I've architected with BigQuery, dbt, and Looker became the foundation for strategic decision-making across organizations.
Work Experience
Analytics Engineer
Wolt - Data & Analytics
- Designed and built a unified payment analytics infrastructure serving as the single source of truth for all payment reporting across multiple business verticals.
- Migrated legacy mart-layer models from fragmented multi-table joins to a scalable unified architecture, improving maintainability and data consistency.
- Implemented payment plan enrichment logic with multipayment detection, enabling accurate classification of complex payment structures.
- Identified and resolved critical data quality issues, including systematic payment amount errors affecting specific markets.
- Developed scalable deduplication key methodology for unified metrics reporting, replacing approaches that hit performance limits at scale.
Analytics Engineer
Hema-Tec
- Migrated a Google AppSheet back end from spreadsheets to BigQuery, creating a scalable data infrastructure for facility operations.
- Built operational dashboards measuring employee performance metrics that enabled data-driven management decisions.
- Automated payroll differential calculations and integrated with the Paylocity API, reducing manual processing time by 90%.
- Developed an automated client reporting system that generates professional PDFs through API integration, eliminating manual report creation.
Senior Analytics Engineer
Self-employed
- Established data warehousing systems for 20+ clients, implementing BigQuery and Snowflake solutions that scaled with business growth.
- Designed ETL/ELT processes using APIs and Webhooks that automated data integration from multiple sources for diverse industries.
- Built advanced forecasting models and KPI tracking systems that enabled data-driven decision making for executive leadership.
- Delivered comprehensive analytics projects including dashboard creation, data modeling, and workflow automation across 200+ engagements.
Data Engineer
Tort Experts
- Established a BigQuery data warehouse infrastructure that enabled efficient data processing and real-time analysis capabilities.
- Leveraged dbt Cloud to build reliable data models that ensured data consistency and accuracy across all reporting layers.
- Automated routine data processes and workflows, improving operational efficiency and reducing manual intervention by 70%.
Analytics Engineer
Ergeon
- Established a BigQuery data warehouse infrastructure that centralized disparate data sources into a unified analytics platform for the entire organization.
- Built comprehensive KPI tracking dashboards that enabled executive leadership to monitor business performance in real-time.
- Streamlined data workflows by automating routine tasks, increasing team productivity and eliminating manual reporting bottlenecks.
Data Analyst
Black Box
- Maintained accuracy within the international product sales database, covering multiple subsidiaries across global markets.
- Created forecasting models that predicted regional sales performance and identified growth opportunities across markets.
- Developed automated reporting processes that streamlined corporate reporting workflows and reduced manual errors.
Experience
BigQuery Data Warehouse Implementation for SaaS Company
Payroll Automation with API Integration
I also integrated the solution with the Paylocity human resources information system via API, eliminating 90% of manual data entry and reducing payroll processing errors to zero. Additionally, I built real-time monitoring dashboards to track payment status and generate compliance reports. The system saved 40+ hours weekly, ensuring accurate, timely payments and regulatory compliance.
Real-time Employee Performance Tracking System
Education
Master’s Degree in Business Administration (MBA)
University of Kentucky - Athens, Greece
Bachelor's Degree in Business Administration
University of West Attica - Athens, Greece
Skills
Libraries/APIs
Google Sheets API, SQLx, REST APIs, WooCommerce API, QuickBooks API, HubSpot API, Pipedrive API
Tools
BigQuery, dbt Cloud, Google Sheets, Google Analytics, Slack, Looker, Microsoft Access, FileMaker, Retool, Microsoft Power BI, Zapier, Stitch Data, Tableau, Google Forms, Jira, Notion, Google Meet, Zoom, Microsoft Excel, Paylocity, Git
Languages
SQL, Google Apps Script, Python, JavaScript, Snowflake, Looker Modeling Language (LookML)
Paradigms
ETL, Business Intelligence (BI)
Platforms
Dataform, Airbyte, Visual Studio Code (VS Code), Google Ads, Bing Ads, Shopify, Mixpanel, WordPress, Windows, Google AppSheet
Storage
Google Cloud, Databases, MySQL, PostgreSQL
Frameworks
Django
Other
Looker Studio, Data Engineering, Data Analytics, Financial Analysis, Teams, Dashboards, Data Visualization, Google BigQuery, CSV, Data Quality Analysis, Metabase, Fivetran, Google Cloud Functions, Product Analytics, Google Search Console, Business, Finance, Google, Key Performance Indicators (KPIs), Data Analysis, Pricing, Monte Carlo, APIs, ELT, Data Modeling, API Integration, Database Automation, Financial Modeling, Data Warehousing, Performance Analysis, Data Build Tool (dbt), Webhooks, Dagster, Payments, Monday.com
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