Master SQL: The Differences Between UNION vs UNION ALL


Master SQL: The Differences Between UNION vs UNION ALL

The important thing to remember about SQL (and UNION vs UNION ALL) is that the structures you design aren’t solely monolithic entities. Databases are dynamic, as the data within them is constantly changing and being added.

One crucial element of manipulating your databases is in the form of a UNION operator. But how does the UNION clause differ from its counterpart, the UNION ALL?

Let’s take a look at use cases for both, what they are intended for, and how you would implement them in your queries and databases.

UNION vs UNION ALL: Side-by-Side Comparison

Only unique recordsYesNo
Allows duplicatesNoYes
Columns neededThe same number of columns are needed on both SELECT statementsThe same number of columns are needed on both SELECT statements
Data types supportedLike data types between SELECT statementsLike data types between SELECT statements
Retrieval orderColumns are retrieved in the order of the SELECT statementAlso retrieved in the same order as the SELECT statement

UNION vs UNION ALL: What’s the Difference?

Both the UNION and UNION ALL operators have similar use cases. Their constraints are identical, but how they return data is slightly different. Where to use these clauses is more of a situational case as opposed to one being preferable over the other.

How Do You Use the UNION or UNION ALL Statement?

UNION and UNION ALL function by combining the results of SELECT statements. SELECT statements themselves are nothing more than queries, as even beginners in SQL should know.

How UNION and UNION ALL have some utility is by allowing for the combination of more than one SELECT statement. This allows for the return of similar data types which is then rendered as a single result.

Computer developer programming language
The UNION operator can be useful in data warehouse applications that use tables.


UNION and UNION ALL only work on identical data types, and the columns queried have to be identical between however many SELECT statements you’re combining.

UNION and UNION ALL are not like a JOIN, however. A JOIN is the combination of two tables and, as such, the syntax is different. UNION and UNION ALL are meant to return results from queries and JOIN, and their variants are meant to combine datatypes in a singular table.

UNION and UNION ALL also differ from a VIEW because that statement is merely displaying specified tables. While you could potentially construct a VIEW query utilizing UNION or UNION ALL, they have vastly different syntax and purposes when used.

Where Do UNION and UNION ALL Differ?

UNION as a statement only returns unique results between two or more SELECT statements. Repeated values aren’t present whenever you select to use UNION. This is handy if you’re trying to go for unique results between two separate SELECT statements, for instance analyzing data from sales and salesperson tables.

UNION ALL, on the other hand, returns duplicate results, meaning you’ll get repeated rows when using it. This has its own use, of course, and, as an example, can be thought of when returning data from a SELECT statement querying a pair of tables with customer and shipping information.

One would expect repeated results considering the data, and both separate queries will likely have some identical values, given that you’ll be shipping to your customers.

Both have their usefulness, of course, and, as stated before, are purely situational. If you’re structuring queries where you need individual results, then UNION is going to be the best candidate. UNION ALL is ideal if the data returned isn’t hindered by duplicated results.

What Are the Requirements for Using UNION and UNION ALL?

The chief thing to keep in mind when deciding to use UNION or UNION ALL is that there are specific requirements needed before using them in a query. However, many SELECT statements will need an identical amount of columns and identical datatypes.

programming code
Unlike UNION, UNION ALL doesn’t ignore duplicate rows.


If you’re looking to combine multiple results between disparate queries, it might be worth looking into using a JOIN statement where the joining constraint is directed towards a shared column despite differing datatypes within.

What this means is that you’re not going to use a UNION or UNION ALL to return dates from one table, and transactions from another. Instead, you’ll be needing to return dates from both tables.

Ignoring this requirement will likely lead to your SQL returning an error, as UNION and UNION ALL will not function when pointed at wildly different tables and datatypes.

UNION vs UNION ALL: 5 Must-Know Facts

  1. UNION is one of the four basic Set Operators utilized in SQL.
  2. UNION interacts solely with SELECT statements.
  3. UNION cannot interact with VIEW or JOIN unless part of a SELECT query.
  4. UNION ALL is faster than UNION.
  5. UNION ALL is identical in function to UNION, minus duplicated results.

UNION vs UNION ALL: Which One Is Better? Which One Should You Use?

There is no explicit winner when using either of these operators. Their use cases differ, but their actual implementation is identical when constructing your queries. UNION is less performant overall, as it does some work behind the scenes to remove duplicate entries from the query’s result. UNION ALL is faster on the whole, but has limited utility if you’re after only distinctive results.

SQL does have best practices, but when using Set Operators you’re likely to use all of them for different purposes. At the end of the day, both of these operators are merely tools that are used to accomplish the various tasks you’ll encounter when running databases.

As such, use either one as needed; there is no clear winner. The only distinction to be made when using either of these SQL operators is whether you need unique results or could stand to have duplicated results returned in your queries.

Master SQL: The Differences Between UNION vs UNION ALL FAQs (Frequently Asked Questions) 

Is SQL easy to learn?

SQL has many tutorials and documentation widely available for its various implementations. Learning SQL is a process, but it isn’t quite as dense a subject as approaching programming C++ or Java. SQL on its own has an express purpose and isn’t meant to program applications necessarily.

That said, SQL is easy to pick up, but it will still require a good bit of effort from any person wishing to learn it. Learning the basics of SQL is a relatively quick endeavor, but using it effectively will require dedicated study and practice.

Is SQL a programming language?

Whether SQL is a programming language or not is a fairly loaded question. What can be said about SQL is that it is a language and vocabulary users leverage to communicate with their computers to accomplish specific tasks. While these tasks aren’t as broad as general programming principles, they do correspond to a particular demand.

With this in mind, SQL is functionally a programming language. Some could argue that it is not Turing complete, but SQL has a specific intended purpose. Whether you consider it a programming language or not will boil down to which definition you choose to apply to programming.

What is SQL intended for?

SQL is a coding language meant for administering databases. This extends to the creation of databases as well as retrieving data from them. SQL as a whole makes creating databases an easy process, provided you’re familiar with the syntax and structure necessary for creating your tables.

Querying is, likewise, a simple task, and only requires knowledge of the different operators needed and when to use them. It isn’t necessarily a complex language, but it certainly encompasses rather complex data sets.

Can you use UNION to create a view in SQL?

UNION is a set operator, and as such has no means of actually creating a view. That specific query would require a VIEW statement, which has differing syntax and use cases. You would use a VIEW to restrict the data returned to a more palatable presentation for someone else to actually read and interpret.


Can you use UNION to combine tables?

UNION can return results from more than one table per the arguments presented in a SELECT statement. UNION as a whole cannot create a wholly new table from two different tables, however.

When combining tables you’ll want to use a JOIN statement which has its own unique requirements and syntax to adhere to. JOIN statements are expressly designed for combining tables with differing or similar data types depending on the operator used.

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