![]() Now that you know how to use both UNION and UNION ALL, you’re probably wondering which one is best for your situation. UNION or UNION ALL – Which Should You Choose? Let’s execute this new query and observe the output: nameĬan you spot all of the duplicate records? Compare this output to our original two tables. With UNION ALL in place, we can expect the results to include duplicates. Now let’s alter the query and change UNION to UNION ALL: There we have it! All of the members from both clubs! Running this query produces the following result: name This follows the rules of using UNION and should execute without an error. You can see that we use columns of the same data type and SELECT the same number of columns in each query. UNION first performs a sorting operation and eliminates the records that are duplicated across all columns before finally returning the combined data set. Using the UNION syntax, we get the following query: Now that we have our tables, let’s write our SQL query. Similarly, the rowing_club contains the name of club members and what location they attend. It contains the name of club members and what location they attend: name Each club may have several different branches or locations where they meet. Each table will show the members of that club and what location they attend. Imagine we have a database with information on several clubs. Let’s look at a practical example to gain greater understanding of UNION vs. This use case is covered in this article on how to join tables without a common column. You can use UNION and UNION ALL to combine tables that do not have any columns in common. Including it with the second query will not cause an error, but it will also have no impact on the output. When using SQL aliases in conjunction with UNION and UNION ALL, you only need to include the alias with the first query.The column names included in both queries can differ when this is the case, the resulting dataset will show the column names from the first query.The number of columns used in your first query and your second query must be the same and the data types (e.g.Failure to adhere to these rules will result in error messages: There are several usage rules for UNION and UNION ALL. Once again, the columns in the SELECT are of the same or matching data types and the WHERE clause is optional: The SQL syntax below shows a UNION ALL occurring between two different tables. Remember, UNION ALL combines the results of two or more SELECT statements, showing all values, including duplicates if they exist. The WHERE clause shown is an optional inclusion: The SQL syntax below shows a UNION occurring between two different tables the columns in both SELECT statements are of the same or matching data types. ![]() Remember, UNION combines the result set of two or more SELECT statements, showing only distinct values. Let’s look at them individually, starting with UNION. The syntax of both UNION variants is very similar. ![]() If you feel like you would benefit from a well-structured, comprehensive course that covers foundational SQL, consider this SQL Basics course from LearnSQL. UNION ALL returns all records, including duplicates. ![]() ![]() UNION ALL, there is one major difference: ![]()
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