Interview Questions and Answers

Aggregate tables store precomputed, summarized data to improve query performance. They contain aggregated values, such as totals or averages, to reduce the need to perform calculations during queries.

Example:

Storing monthly sales totals in an aggregate table to accelerate queries related to sales performance.

A snowflake schema is a type of dimensional modeling in which dimension tables are normalized into multiple related tables, forming a shape resembling a snowflake. It is used for reducing redundancy in the data warehouse schema.

Example:

In a snowflake schema, a dimension table like 'Region' may be normalized into sub-dimensions like 'Country' and 'City.'

Performance optimization in a Data Warehouse involves techniques such as indexing, partitioning, aggregations, and proper data modeling. It also includes hardware considerations, query optimization, and ETL process tuning.

Example:

Creating indexes on frequently queried columns to speed up data retrieval in a large data warehouse.

Data lineage refers to the tracking and visualization of the flow of data from its origin through various transformations and into the data warehouse. It helps in understanding the data's path and ensuring data quality.

Example:

A data lineage diagram illustrating how customer data flows from source systems, through ETL processes, and into the data warehouse.

Slowly changing facts refer to the handling of changes in the measured values (facts) over time in a data warehouse. It involves managing updates or inserts to maintain historical accuracy in the facts.

Example:

Updating the sales quantity in a fact table to reflect changes over time due to corrections or adjustments.

Indexing involves creating data structures to quickly locate and retrieve rows from tables. In a data warehouse, proper indexing can significantly improve query performance by reducing the amount of data that needs to be scanned.

Example:

Creating indexes on columns frequently used in WHERE clauses to accelerate data retrieval in a data warehouse.