Difference between Union and Union All in Tableau?

 In Tableau, the Union and Union All operations are used to combine data from multiple tables or data sources. However, there is a key difference between the two:

Union: 

The Union operation in Tableau combines data from multiple tables or queries and removes duplicate rows. It creates a single result set that includes all unique rows from the combined tables. In other words, Union performs deduplication, ensuring that duplicate records are eliminated.

For example, if Table A has 100 records and Table B has 150 records, a Union operation between these two tables will result in a combined table with 250 unique records (assuming there are no duplicate rows within each table).

Union All: 

The Union All operation, on the other hand, also combines data from multiple tables or queries, but it does not remove duplicate rows. It simply concatenates all rows from the combined tables, including duplicate records. Union All preserves all rows, regardless of whether they are duplicated or not.

Using the same example as above, a Union All operation between Table A and Table B will result in a combined table with 250 records, including any duplicate rows.

In summary, Union combines data from multiple tables or queries and removes duplicates, resulting in a combined table with unique records. Union All combines data without removing duplicates, simply concatenating all rows from the combined tables. The choice between Union and Union All depends on whether you want to preserve duplicate rows or remove them during the data combination process.

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