You have a few choices for combining data from different sources. Choosing whether to employ JOINS or UNIONS is one of such alternatives. However, before choosing one over the other, you must first grasp how they integrate data.

What are SQL UNIONS?

Use the UNION operator to merge the results of two or more SELECT queries into a single result set. Using joins to connect columns from two tables is not the same as using the union operation. The union operation merges all rows from two source tables into a single result table, stacking them on top of one another.

These are the essential principles for using UNION to combine the result sets of two SELECT queries:

In all queries, the number and order of the columns must be the same.

The associated columns’ data types must be compatible.

The tables are union-compatible if specific requirements are met:


The fundamental syntax of UNION is as follows:


Let’s imagine that specific hypothetical fields in our workers’ and customers’ tables, such as first name and last name, exist to comprehend the union operation better.

To aggregate the results of two searches, use a union operation.

The following statement returns all of the customers’ and workers’ first and last names:

SQL UNION vs JOIN example

SQL JOINS, what are they?

You work at a company that collects data, and you need to know what that data means to gain a clear picture. SQL JOIN clauses can assist you in identifying the relevant data in your information if there are duplicate entries. JOIN clauses in SQL are ideal for joining rows from two or more tables and the standard fields between them.

A logical combination of two SQL tables is referred to as a SQL join. There are several methods for joining tables together, the most frequent of which are locating similar values between them. Normalization is made feasible through SQL joins, which allow searches to provide results that span many tables.

The syntax is as follows:

SELECT column_name FROM table1 JOIN table2

SQL JOINS come in a variety of forms:

  • RIGHT JOIN and

JOINS, to put it simply, merge data into new columns. A “join condition” is used in the query to connect columns to create new rows. The new rows are made up of values from both tables’ columns. UNIONS join two or more rows of data to create a new row. The union, in this case, takes the result as rows and appends them row by row.

What is the difference between join and union in SQL?

In a union, rows are merged rather than columns to produce results. Both joins and unions can be employed to aggregate data from one or more tables into a single result. They use different approaches to this. A join combines columns from separate tables, whereas a union joins rows together.

Join unites columns from separate tables together, whereas union joins rows together. If you see it in your imagination, it looks like this: With a full outer join, you may add columns to your result rows (tuples) and broaden them with columns (attributes) from the source tables’ rows (tuples).

Comparing SQL UNION and JOIN Statements

ParameterJOIN in SQLUNION in SQL
EssentialsWhen two tables’ relations have a common attribute or field, the JOIN clause merges their tuples and attributes.The UNION clause merges the tuples of all the relations found in the query.
CategoriesThe LEFT, RIGHT, FULL OUTER, and INNER JOINS are the four primary forms of JOIN clauses.The LEFT, RIGHT, FULL OUTER, and INNER JOINS are the four primary forms of JOIN clauses.
When they can be applied  We can only use the JOIN clause when the two relations involved have one attribute (at least) in common.We can use the UNION clause when the total number of columns in a query is the same while the corresponding attribute has a similar domain.
EffectThe resultant tuple obtained after applying the JOIN clause turns out to be more than that of the length of those tuples that we involved in the relations.The total number of resultant tuples obtained after applying the UNION clause is always more when compared to the tuples present in both the relations of a query.

Major Differences Between JOIN and UNION in SQL

  • The JOIN clause is applicable only when the two relations involved have at least one attribute common in both. On the other hand, the UNION is appropriate when the two relations have the same number of attributes and the domains of corresponding attributes are the same.
  • The primary difference between JOIN and UNION is that JOIN combines the tuples from two relations and the resultant tuples include attributes from both the relations. On the other hand, the UNION combines the result of two SELECT queries.
  • The resulting tuple in JOIN is more extensive since it contains attributes from both relations. On the other hand, UNION increases the number of tuples since it includes the tuple from both of the query’s relations.
  • There are four different kinds of JOIN. They are INNER, LEFT, RIGHT, and FULL OUTER JOIN. However, there are two different kinds of UNION: UNION and UNION ALL.

Final Words

Both are data combining procedures that are employed in many scenarios. When we wish to combine characteristics from two relations that share at least one attribute, we utilize JOIN. When we want to combine the tuples of two relations within the query, we use UNION.

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