In Power BI, Merge queries and Append queries are two methods of combining data from multiple tables or data sources. Here are the main differences between both-
Merge Queries: Merge queries combine two or more queries by matching values in specified columns. It is similar to SQL join operation.
You can choose to merge queries using Inner Join, Left Outer Join, Right Outer Join or Full Outer Join. Merge queries are useful when you have related data in different tables and need to combine them into a single table or data source.
Append queries: Append queries combines two or more queries by appending the rows from one query to the end of another query. This is similar to a SQL union operation.
The column names and data types in the two queries must match for an append operation to be successful. Append queries are useful when you have similar data in multiple tables and want to combine them into a single table or data source.
There are some important differences between merge queries and join queries in Power BI:
- Merge queries combine tables horizontally, while append queries combine tables vertically.
- Merge queries require at least one matching column in each table, while append queries require matching columns with the same data types.
- Merge queries can combine tables with different numbers of columns, while append queries require tables to have the same number of columns.
- Merge queries can be used to create new columns based on the matching values, while append queries do not create new columns.
In short, use merge queries when you need to combine related data from different tables, and use append queries when you need to combine similar data from different tables.
Refer more – interview questions and Answers