Which is faster union or union all?

Which is faster union or union all?

UNION ALL is always FASTER… As we all know that, UNION and UNION ALL are the SET operators which combines/merges the multiple data sets data into a single data set. UNION eliminates the duplicates after combining the records.

What does Union all mean?

The SQL UNION ALL operator is used to combine the result sets of 2 or more SELECT statements. It does not remove duplicate rows between the various SELECT statements (all rows are returned). Each SELECT statement within the UNION ALL must have the same number of fields in the result sets with similar data types.

Does Union all remove duplicates?

Union will remove duplicates. Union All does not. That you don't have already the duplicates in the first part of the query (maybe generated by the left join). As I understand it UNION it will not add to the result set rows that are already on it, but it won't remove duplicates already present in the first data set.

What is Union in Oracle with example?

The Oracle UNION operator is used to combine the result sets of 2 or more Oracle SELECT statements. It removes duplicate rows between the various SELECT statements. Each SELECT statement within the UNION operator must have the same number of fields in the result sets with similar data types.