There are several differences between a Union and a Union All. While they both create a relationship between two tables, the way they go about it is different. A Union will remove duplicates from the data while a Union All will not. Additionally, a Union can only include columns that are found in both tables, while a Union All can include columns that are only found in one table. Understanding the difference between these two types of unions is important when designing your SQL queries.
What is Union?
Union is a SQL keyword that is used to combine the results of two or more queries into a single result set. The Union operator removes duplicate rows from the result set. Union is typically used to combine data from multiple tables, but it can also be used with data from a single table. For example, Union can be used to combine the results of multiple SELECT statements into a single result set.
The union can also be used to combine the results of two or more queries that use different WHERE conditions. In this case, Union will return all rows from both queries, even if some of the rows are duplicates. Union has a number of advantages over other SQL keywords, such as JOIN and UNION ALL. Union is easier to use than JOIN, and it does not require the user to have knowledge of relational algebra. Union is also faster than UNION ALL, and it uses less memory.
What is Union All?
Union All is an SQL operator that combines the results of two or more query expressions into a single result set. Unlike Union, Union All does not eliminate duplicate rows. Union All can be used to combine the results of unrelated queries, or it can be used to execute multiple queries on the same table and return all the results. Union All is particularly useful when working with large data sets, as it can help to improve performance by reducing the number of times the data needs to be read from the database. Union All is also commonly used in conjunction with other operators, such as GROUP BY and ORDER BY, to further manipulate the data.
Difference between Union and Union All
Union and Union All are both SQL commands that combine the results of two or more queries into a single result set. The Union command removes duplicate rows from the combined result set, while Union All includes all rows, even duplicates. Union is typically used when you want to ensure that there are no duplicate rows in the final result set. Union All is faster than Union since it doesn’t need to scan the combined result set for duplicates. However, Union All can return duplicate rows, so it’s important to be aware of that before using this command.
Conclusion
If you’re still unsure of the difference between Union and Union All, don’t worry. We’ve put together a quick summary of the two commands below. Union removes duplicate rows from the result set while Union All keeps them. Union is faster than Union All because it doesn’t have to compare every row in the data sets. However, Union All will give you a larger result set.
