SQL-Based Data Validation and Anomaly Detection

Techniques for validating data quality and detecting anomalies using SQL: identifying nulls and missing values, finding duplicates and orphan records, range checks, sanity checks across aggregates, distribution checks, outlier detection heuristics, reconciliation queries across systems, and building SQL based alerts and integrity checks. Includes strategies for writing repeatable validation queries, comparing row counts and sums across pipelines, and documenting assumptions for investigative analysis.

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Data Lake and Warehouse Architecture

Designing scalable data platforms for analytical and reporting workloads including data lakes, data warehouses, and lakehouse architectures. Key topics include storage formats and layout including columnar file formats such as Parquet and table formats such as Iceberg and Delta Lake, partitioning and compaction strategies, metadata management and cataloging, schema evolution and transactional guarantees for analytical data, and cost and performance trade offs. Cover ingestion patterns for batch and streaming data including change data capture, data transformation approaches and compute engines for analytical queries, partition pruning and predicate pushdown, query optimization and materialized views, data modeling for analytical workloads, retention and tiering, security and access control, data governance and lineage, and integration with business intelligence and real time analytics. Also discuss operational concerns such as monitoring, vacuuming and compaction jobs, metadata scaling, and strategies for minimizing query latency while controlling storage cost.

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Data Quality and Edge Case Handling

Practical skills and best practices for recognizing, preventing, and resolving real world data quality problems and edge cases in queries, analyses, and production data pipelines. Core areas include handling missing and null values, empty and single row result sets, duplicate records and deduplication strategies, outliers and distributional assumptions, data type mismatches and inconsistent formatting, canonicalization and normalization of identifiers and addresses, time zone and daylight saving time handling, null propagation in joins, and guarding against division by zero and other runtime anomalies. It also covers merging partial or inconsistent records from multiple sources, attribution and aggregation edge cases, group by and window function corner cases, performance and correctness trade offs at scale, designing robust queries and pipeline validations, implementing sanity checks and test datasets, and documenting data limitations and assumptions. At senior levels this expands to proactively designing automated data quality checks, monitoring and alerting for anomalies, defining remediation workflows, communicating trade offs to stakeholders, and balancing engineering effort against business risk.

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Data Quality and System Integration Challenges

Focuses on data integrity, governance, and the operational issues that arise when data moves between systems. Candidates should be able to identify common data quality problems such as duplicates, missing or inconsistent fields, formatting mismatches, schema drift, and validation gaps. Understand how those issues propagate through integration pipelines and impact reporting, analytics, forecasting, and other downstream processes. Discuss reconciliation strategies, validation rules, data cleansing, deduplication, master data management patterns, monitoring and alerting for data anomalies, and policies for schema evolution and versioning. Also cover practical approaches to prevent and remediate integration induced data errors and how to prioritize data quality work across cross-system business workflows (for example, CRM/billing integrations, HR and compensation data feeds, marketing automation pipelines, or product analytics), not just any single business function.

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Data Architecture and Pipelines

Designing data storage, integration, and processing architectures. Topics include relational and NoSQL database design, indexing and query optimization, replication and sharding strategies, data warehousing and dimensional modeling, ETL and ELT patterns, batch and streaming ingestion, processing frameworks, feature stores, archival and retention strategies, and trade offs for scale and latency in large data systems.

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Data Cleaning and Quality Validation in SQL

Handle NULL values, duplicates, and data type issues within queries. Implement data validation checks (row counts, value distributions, date ranges). Practice identifying and documenting data quality issues that impact analysis reliability.

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Big Data Technologies Stack

Overview of big data tooling and platforms used for data ingestion, processing, and analytics at scale. Includes frameworks and platforms such as Apache Spark, Hadoop ecosystem components (HDFS, MapReduce, YARN), data lake architectures, streaming and batch processing, and cloud-based data platforms. Covers data processing paradigms, distributed storage and compute, data quality, and best practices for building robust data pipelines and analytics infrastructure.

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Data Cleaning and Business Logic Edge Cases

Covers handling data centric edge cases and complex business rule interactions in queries and data pipelines. Topics include cleaning and normalizing data, handling nulls and type mismatches, deduplication strategies, treating inconsistent or malformed records, validating results and detecting anomalies, using conditional logic for data transformation, understanding null semantics in SQL, and designing queries that correctly implement date boundaries and domain specific business rules. Emphasis is on producing robust results in the presence of imperfect data and complex requirements.

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Data Quality and Real World Constraints

Addresses how to work with imperfect real world data and operational constraints. Topics include diagnosing and handling missing data and outliers, dealing with label noise and class imbalance, detecting and reacting to data drift, designing robust features and sampling strategies, ensuring data provenance and lineage, instrumentation for reliable signal collection, and making trade offs given latency, privacy, or cost constraints.

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Segmentation and Personalization at Scale

Designing segmentation and personalization strategies for very large audiences while balancing correctness, performance, and privacy. Topics include static and dynamic segment design, real time versus batch updates, indexing and query strategies for efficient audience selection, overlap and exclusion logic, orchestration of personalization across channels, attribute and behavioral scoring, propensity and affinity models, consistency guarantees, frequency capping, privacy and consent-aware personalization, integration with decisioning systems, and operational practices for testing and validating personalized experiences at scale.

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Event Driven Architectures for Marketing

Designing and operating event driven systems for marketing workflows and real time activation. Key areas include event schema design and governance change data capture and streaming ingestion patterns event routing and transformation layers message broker selection and partitioning strategies handling idempotency duplication and ordering guarantees real time feature generation for personalization and scoring model serving latency considerations downstream activation to advertising and campaign systems monitoring observability and operational runbooks for replay backpressure and schema evolution. Candidates should be able to discuss trade offs for latency throughput and operational complexity when building event driven marketing pipelines.

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Data Processing and Transformation

Focuses on algorithmic and engineering approaches to transform and clean data at scale. Includes deduplication strategies, parsing and normalizing unstructured or semi structured data, handling missing or inconsistent values, incremental and chunked processing for large datasets, batch versus streaming trade offs, state management, efficient memory and compute usage, idempotency and error handling, and techniques for scaling and parallelizing transformation pipelines. Interviewers may assess problem solving, choice of algorithms and data structures, and pragmatic design for reliability and performance.

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Data Quality and Validation

Covers the core concepts and hands on techniques for detecting, diagnosing, and preventing data quality problems. Topics include common data issues such as missing values, duplicates, outliers, incorrect labels, inconsistent formats, schema mismatches, referential integrity violations, and distribution or temporal drift. Candidates should be able to design and implement validation checks and data profiling queries, including schema validation, column level constraints, aggregate checks, distinct counts, null and outlier detection, and business logic tests. This topic also covers the mindset of data validation and exploration: how to approach unfamiliar datasets, validate calculations against sources, document quality rules, decide remediation strategies such as imputation quarantine or alerting, and communicate data limitations to stakeholders.

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Data Pipelines and Feature Platforms

Designing and operating data pipelines and feature platforms involves engineering reliable, scalable systems that convert raw data into production ready features and deliver those features to both training and inference environments. Candidates should be able to discuss batch and streaming ingestion architectures, distributed processing approaches using systems such as Apache Spark and streaming engines, and orchestration patterns using workflow engines. Core topics include schema management and evolution, data validation and data quality monitoring, handling event time semantics and operational challenges such as late arriving data and data skew, stateful stream processing, windowing and watermarking, and strategies for idempotent and fault tolerant processing. The role of feature stores and feature platforms includes feature definition management, feature versioning, point in time correctness, consistency between training and serving, online low latency feature retrieval, offline materialization and backfilling, and trade offs between real time and offline computation. Feature engineering strategies, detection and mitigation of distribution shift, dataset versioning, metadata and discoverability, governance and compliance, and lineage and reproducibility are important areas. For senior and staff level candidates, design considerations expand to multi tenant platform architecture, platform application programming interfaces and onboarding, access control, resource management and cost optimization, scaling and partitioning strategies, caching and hot key mitigation, monitoring and observability including service level objectives, testing and continuous integration and continuous delivery for data pipelines, and operational practices for supporting hundreds of models across teams.

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Data Collection and Instrumentation

Designing and implementing reliable data collection and the supporting data infrastructure to power analytics and machine learning. Covers event tracking and instrumentation design, decisions about what events to log and schema granularity, data validation and quality controls at collection time, sampling and deduplication strategies, attribution and measurement challenges, and trade offs between data richness and cost. Includes pipeline and ingestion patterns for real time and batch processing, scalability and maintainability of pipelines, backfill and replay strategies, storage and retention trade offs, retention policy design, anomaly detection and monitoring, and operational cost and complexity of measurement systems. Also covers privacy and compliance considerations and privacy preserving techniques, governance frameworks, ownership models, and senior level architecture and operationalization decisions.

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Data Manipulation and Transformation

Encompasses techniques and best practices for cleaning, transforming, and preparing data for analysis and production systems. Candidates should be able to handle missing values, duplicates, inconsistency resolution, normalization and denormalization, data typing and casting, and validation checks. Expect discussion of writing robust code that handles edge cases such as empty datasets and null values, defensive data validation, unit and integration testing for transformations, and strategies for performance and memory efficiency. At more senior levels include design of scalable, debuggable, and maintainable data pipelines and transformation architectures, idempotency, schema evolution, batch versus streaming trade offs, observability and monitoring, versioning and reproducibility, and tool selection such as SQL, pandas, Spark, or dedicated ETL frameworks.

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Analytics Infrastructure and Query Performance

Designing analytics data infrastructure and optimizing query performance for analytics workloads. Includes data modeling for analytics, columnar versus row storage trade offs, clustering and partitioning strategies, indexing and materialized views, caching and result reuse, profiling and tuning slow queries, cost and latency trade offs for large scale analytics, and considerations for ingest pipelines and analytical storage choices.

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Data Transformation and Preparation

Focuses on the technical skills and judgement required to connect to data sources, clean and shape data, and prepare datasets for analysis and visualization. Includes identifying necessary transformations such as calculations, aggregations, filtering, joins, and type conversions; deciding whether to perform transformations in the business intelligence tool or in the data warehouse or database layer; designing efficient data models and extract transform load workflows; ensuring data quality, lineage, and freshness; applying performance optimization techniques such as incremental refresh and pushdown processing; and familiarity with tools and features such as Power BI Power Query, Tableau data preparation capabilities, and structured query language for database level transformations. Also covers documentation, reproducibility, and testing of data preparation pipelines.

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Data Quality and Anomaly Detection

Focuses on identifying, diagnosing, and preventing data issues that produce misleading or incorrect metrics. Topics include spotting duplicates, missing values, schema drift, logical inconsistencies, extreme outliers caused by instrumentation bugs, data latency and pipeline failures, and reconciliation differences between sources. Covers validation strategies such as data tests, checksums, row counts, data contracts, invariants, and automated alerting for quality metrics like completeness, accuracy, and timeliness. Also addresses investigation workflows to determine whether anomalies are data problems versus true business signals, documenting remediation steps, and collaborating with engineering and product teams to fix upstream causes.

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Real Time and Batch Ingestion

Focuses on choosing between batch ingestion and real time streaming for moving data from sources to storage and downstream systems. Topics include latency and throughput requirements, cost and operational complexity, consistency and delivery semantics such as at least once and exactly once, idempotent and deduplication strategies, schema evolution, connector and source considerations, backpressure and buffering, checkpointing and state management, and tooling choices for streaming and batch. Candidates should be able to design hybrid architectures that combine streaming for low latency needs with batch pipelines for large backfills or heavy aggregations and explain operational trade offs such as monitoring, scaling, failure recovery, and debugging.

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Data and Technical Strategy Alignment

Evaluates a candidate's ability to reason about the technical and architectural trade-offs that shape a data platform: batch versus streaming (and hybrid) pipelines, data warehouse versus data lake versus lakehouse architecture, ETL versus ELT, schema design and partitioning for analytics and ingestion, data contracts between producers and consumers, feature stores, and metrics (semantic) layers. Good answers pick a concrete architecture or approach for a stated scale, latency, and cost profile, name the trade-offs of the alternatives, and justify the choice rather than reciting definitions.

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Data Quality Debugging and Root Cause Analysis

Focuses on investigative approaches and operational practices used when data or metrics are incorrect. Includes techniques for triage and root cause analysis such as comparing to historical baselines, segmenting data by dimensions, validating upstream sources and joins, replaying pipeline stages, checking pipeline timing and delays, and isolating schema change impacts. Candidates should discuss systematic debugging workflows, test and verification strategies, how to reproduce issues, how to build hypotheses and tests, and how to prioritize fixes and communication when incidents affect downstream consumers.

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Data Transformation and Loading

Focuses on the extract transform load and extract load transform approaches for ingesting transforming and loading data. Candidates should understand three core stages: extract which is acquiring data from sources such as application programming interfaces databases logs and message queues; transform which is cleaning validating reshaping aggregating and enriching data to meet downstream requirements; and load which is writing processed data to targets such as analytic databases data warehouses data lakes or reporting systems. Topics include the differences between extract transform load and extract load transform, incremental loads versus full refresh, scheduling and orchestration best practices, tooling and frameworks used for transformation and orchestration, idempotency and deduplication strategies, error handling and retry semantics, data quality checks end to end validation recovery and integration with business intelligence and analytics consumers. Interview focus is on concrete transformation logic pipeline orchestration and validation strategies and on choosing the right pattern and tooling for given constraints.

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Data and Analytics Infrastructure

Designing, building, and operating end-to-end data and analytics platforms that collect, transform, store, and serve event, product, and revenue data for reporting, analysis, and decision making. Core areas include event instrumentation and tag management to capture user journeys, marketing attribution, and experimental events; data ingestion strategies and connectors; extract-transform-load (ETL/ELT) pipelines and streaming processing; orchestration and workflow management; and the trade-offs between batch and real-time architectures. Candidates must be able to design storage and serving layers, including data warehouses, data lakes, lakehouse patterns, and managed analytical databases, and to choose storage formats, partitioning, and indexing strategies driven by volume, velocity, variety, and access patterns. Data modeling for analytics covers raw event layers, curated semantic layers, dimensional modeling, and metric definitions that support business intelligence and product analytics. Governance and reliability topics include data quality validation, freshness monitoring, lineage, metadata and cataloging, schema evolution, master data considerations, and role-based access control. Operational concerns include scaling storage, processing, and query concurrency; fault tolerance and resiliency; monitoring, observability, and alerting; and cost, performance, and capacity planning trade-offs. Finally, candidates should be able to evaluate and select tools and frameworks for orchestration, stream processing, and business intelligence; integrate analytics platforms with downstream consumers; and explain how architecture and operational choices support marketing, product, and business decisions while balancing tooling investment and team skills.

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Data and Artificial Intelligence Concepts

Core data engineering and applied AI/ML concepts spanning the full data-to-model lifecycle. Covers data modeling, data warehouse versus data lake trade offs, batch versus real time processing, streaming and event driven pipelines, extract transform load (ETL) and extract load transform (ELT) approaches, and analytics and reporting patterns including key performance indicator and metric design. On the machine learning side, covers model training, validation, and inference, feature engineering, model deployment and monitoring, and machine learning operations (MLOps) and governance. Candidates should be able to reason about how these architectural and modeling choices affect latency, cost, and accuracy, and to communicate the resulting technical trade offs and risks clearly to non-technical stakeholders.

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Apache Spark Distributed Processing and Optimization

Comprehensive knowledge of processing large datasets across a cluster and practical techniques for optimizing end to end data pipelines in Apache Spark. Candidates should understand distributed computation patterns such as MapReduce and embarrassingly parallel workloads, how work is partitioned across tasks and executors, and how partitioning strategies affect data locality and performance. They should explain how and when data shuffles occur, why shuffles are expensive, and how to minimize shuffle cost using narrow transformations, careful use of repartition and coalesce, broadcast joins for small lookup tables, and map side join approaches. Coverage should include join strategies and broadcast variables, avoiding wide transformations, caching versus persistence trade offs, handling data skew with salting and repartitioning, and selecting effective partition keys. Resource management and tuning topics include executor memory and overhead, cores per executor, degree of parallelism, number of partitions, task sizing, and trade offs between processing speed and resource usage. Fault tolerance and scaling topics include checkpointing, persistence for recovery, and strategies for horizontal scaling. Candidates should also demonstrate monitoring, debugging, and profiling skills using the Spark UI and logs to diagnose shuffles, stragglers, and skew, and to propose actionable tuning changes and coding patterns that scale in distributed environments.

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Data Pipeline Architecture

Design end to end data pipeline solutions from problem statement through implementation and operations, integrating ingestion transformation storage serving and consumption layers. Topics include source selection and connectors, ingestion patterns including batch streaming and micro batch, transformation steps such as cleaning enrichment aggregation and filtering, and loading targets such as analytic databases data warehouses data lakes or operational stores. Cover architecture patterns and trade offs including lambda kappa and micro batch, delivery semantics and fault tolerance, partitioning and scaling strategies, schema evolution and data modeling for analytic and operational consumers, and choices driven by freshness latency throughput cost and operational complexity. Operational concerns include orchestration and scheduling, reliability considerations such as error handling retries idempotence and backpressure, monitoring and alerting, deployment and runbook planning, and how components work together as a coherent maintainable system. Interview focus is on turning requirements into concrete architectures, technology selection, and trade off reasoning.

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Metric Definition and Implementation

End to end topic covering the precise definition, computation, transformation, implementation, validation, documentation, and monitoring of business metrics. Candidates should demonstrate how to translate business requirements into reproducible metric definitions and formulas, choose aggregation methods and time windows, set filtering and deduplication rules, convert event level data to user level metrics, and compute cohorts, retention, attribution, and incremental impact. The work includes data transformation skills such as normalizing and formatting date and identifier fields, handling null values and edge cases, creating calculated fields and measures, combining and grouping tables at appropriate levels, and choosing between percentages and absolute numbers. Implementation details include writing reliable structured query language code or scripts, selecting instrumentation and data sources, considering aggregation strategy, sampling and margin of error, and ensuring pipelines produce reproducible results. Validation and quality practices include spot checks, comparison to known totals, automated tests, monitoring and alerting, naming conventions and versioning, and clear documentation so all calculations are auditable and maintainable.

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Experimentation Platforms and Infrastructure

Addresses the technical and organizational infrastructure required to run experiments at scale. Topics include randomization and assignment strategies, traffic allocation, instrumentation and metric collection pipelines, experiment configuration and rollout systems, experiment tracking and metadata, data quality and monitoring, guardrails to detect interference or contamination, automated validity checks, self service experimentation tooling, governance and permissions, and approaches to scale experimentation across many teams while preserving statistical validity. Senior conversations include designing experiment platforms, enabling self service and observability, and trade offs when scaling experiment velocity across products.

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Data Engineering & Analytics Infrastructure Topics

SQL-Based Data Validation and Anomaly Detection

Data Lake and Warehouse Architecture

Data Quality and Edge Case Handling

Data Quality and System Integration Challenges

Data Architecture and Pipelines

Data Cleaning and Quality Validation in SQL

Big Data Technologies Stack

Data Cleaning and Business Logic Edge Cases

Data Quality and Real World Constraints

Segmentation and Personalization at Scale

Event Driven Architectures for Marketing

Data Processing and Transformation

Data Quality and Validation

Data Pipelines and Feature Platforms

Data Collection and Instrumentation

Data Manipulation and Transformation

Analytics Infrastructure and Query Performance

Data Transformation and Preparation

Data Quality and Anomaly Detection

Real Time and Batch Ingestion

Data and Technical Strategy Alignment

Data Quality Debugging and Root Cause Analysis

Data Transformation and Loading

Data and Analytics Infrastructure

Data and Artificial Intelligence Concepts

Apache Spark Distributed Processing and Optimization

Data Pipeline Architecture

Metric Definition and Implementation

Experimentation Platforms and Infrastructure