POWER BI -DATA MODELLING ,RELATIONSHIPS AND JOINS

Power BI is a platform that collects, cleans, analyzes, and presents data from multiple sources in interactive dashboards and reports to aid decision making. Key concepts that make these reports interactive and insightful include data modeling, relationships, and joins.

Data modeling in Power BI organizes data into tables and defines relationships between them. A well-designed data model allows for better filtering, analysis, and summarization of data, creating meaningful and elaborate reports. It helps improve data quality, reduce errors, and organize data for better reporting. There are three approaches to data modeling: flat table, star schema, and snowflake schema.

The flat table approach contains all data in a single table without relationships, making it simple but resulting in data redundancy and poor performance. The star schema, recommended and standard approach, features a fact table at the center surrounded by dimensional tables, offering ease of understanding, low model complexity, and fast performance. The snowflake schema further breaks down dimensional tables into smaller related tables, resulting in less data redundancy but with increased complexity and slower queries.

Facts tables store specific events or transactions to be analyzed, while dimensional tables provide context to these events, such as who, where, and when. Relationships in Power BI are logical connections between tables using primary and foreign keys, allowing filters to flow and avoiding physical merging of tables. Primary keys are unique identifiers in dimension tables, while foreign keys are primary keys in fact tables.

Power BI supports various join types, including inner join, left outer join, right outer join, full outer join, left anti-join, and right anti-join. Power Query joins increase table size and cause redundancy, while Power BI relationships keep data normalized and are more efficient. Power Query joins are used during data loading and transformation, while Power BI relationships are used after data loading in the model view.