SQL Union vs. Join: Combining Data in Different Ways

SQL is a standard language that helps in the easy storage, retrieval, management, or manipulation of data. In SQL, we combine data from two or more tables to achieve the desired outcomes. The data can be combined using two clauses, i.e., UNION and Join. Learn about SQL UNION vs. Join and their attributes to combine data from multiple tables through this article.

Here is what we’ll cover in this article:

• Understanding UNION in SQL
• Types of UNION in SQL
• Understanding Join in SQL
• Types of Join in SQL
• UNION vs. Join in SQL: Key Differences
• Gear Up your Performance with Interview Kickstart
• FAQs

Understanding UNION in SQL

The UNION in SQL refers to a clause that aids in combining data obtained from the outcome of two or more SELECT command queries into one dataset. While combining data, the UNION clause eliminates the duplicate values or data that exist in the combined outcome. 

For instance, if there are two tables, table A and Table B, Table 1 holds a list of four candidates working on sterilizing the sample, and Table 2 holds the list of four candidates who are trypsinizing the sample. Suppose candidates 3 and 4 are common in both events. The outcome will be sequentially: 1, 2, 3, 4,  5, and 6.

Table 1:

Table 2: 

Table 3: The outcome using the UNION clause in SQL will be:

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Types of UNION in SQL

UNION can be used with a variation to change the obtained result. The sole usage of the UNION operator provides unique values, while the usage of ‘UNION ALL’ offers duplicate values as well. The ‘UNION ALL’ combined all the values from the original tables. 

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Understanding Join in SQL

Join in SQL refers to a clause that aids in combining data or rows from two or more tables with respect to the linked columns. It means combining data, values, or information of the database from multiple tables that have common or related information, values, or data in the same database. Database refers to a collection of tables having distinct information data or values. Join in SQL can retrieve information from multiple tables in just one query rather than multiple queries. 

Types of Join in SQL

There are two types of Joins in SQL, i.e., 

1. Inner Join

An SQL Inner Join refers to the type of Join that retrieves the common data from two or more tables. It means It combines two or more tables and delivers only the matching or common response in the outcome. For instance, a classroom has 50 students, each assigned with unique enrollment IDs written in a table. You can combine the table with different classes' tables with enrollment IDs and retrieve a new dataset in outcome, which is a combined dataset of a database.

2. Outer Join

Outer Joins refers to the retrieval of matching and unmatching rows, data, information, or values from two or more tables. It means the outcomes include unmatching rows or data of one table or both tables. The outer Join methods can be categorized into three types:

1. Left Outer Join: Here, the Join retrieves all the data from the left rows of the tables along with the matching data from the rows of the right table. In case there are no matching rows in the right table, the outcome will be delivered as Null.

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2. Right Outer Join: It is similar to the left outer Join, but here, the left term is exchanged by the right. The right outer Join retrieves all the data from the rows of the right table and only the matching data from the rows of the left table. In case there are no matching rows in the left table, the value returned by the Join will be null.

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3. Full Outer Join: The Join reverts the outcome that contains the combined result of both the left outer Join and the right outer Join. Here, the data retrieved holds all the rows from both the tables. It means matching and unmatching values are delivered in the outcome of full outer Join. In case there are no matching values, the outcome will be delivered as null.

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UNION SQL vs. Join: Key Differences

Let us understand the key difference between SQL UNION vs. Join through the following table.

Table 4: UNION vs. Join SQL

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Learning about UNION vs. Join in SQL plays an important role in communicating with databases. These aspects make data management and retrieval easy in SQL. Thus, the demand for skilled professionals in SQL is high. However, with the demand, the competition has increased. 

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FAQs on SQL UNION vs. Join

Q1. Can I use Join instead of UNION?

When it comes to SQL Join vs. UNION, Joins are applicable to combine multiple tables. On the other hand, UNION helps in combining two or more SELECT statements. It means in Join, columns must be common, while in UNION, columns and attributes must be the same.

Q2. Does the UNION clause add duplicates?

When comparing UNION vs. Join SQL, unlike Join, the UNION clause does not permit duplicity in the outcome.

Q3. Is UNION faster in SQL?

Union All tends to be faster in comparison to UNION clauses.

Q4. What is the difference between UNION and full Join?

UNION combines data to create new rows. In contrast, full Join retrieves data from both tables into new columns.

Q5. Which SQL Join is the fastest?

Left outer Joins tend to show better speed and performance in SQL in the majority of the cases.

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