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Difference Between Left Join and Left Outer Join in SQL

Difference Between Left Join and Left Outer Join in SQL

A database consists of an organized collection of structured information usually stored electronically in a computer system. Several different databases, such as SQL Server, Oracle, PostgreSQL, and MySQL, typically use a language to manage data.

One such language is known as SQL. SQL has different Joins commands in the form of Inner Join, Left Join, and Right Join.

As you may know, a Join in SQL is used to assemble rows from two or more tables from the related column. This may raise a question on what do other variations do.

It’s a little confusing, I’m sure! But don’t worry, I’ll provide a detailed account of what they are what they mean, and hopefully, that’ll help you understand better.

Let’s get to it!

What is SQL?

SQL stands for Structured Query Language. This is a language used by various databases for writing and querying data. It allows to manage information using tables and displays a language to query these tables and other related objects, such as views, functions, procedures, etc.

Donald Chamberlin and Raymond Boyce are the designers of SQL, which they made to manipulate data. Their model was based on the works of Edgar Frank Codd, who worked for IBM and invented the relational database in the 70s.

Initially, it was named SEQUEL, but it was shortened to SQL due to specific trademark issues. However, you can still call them SEQUEL if you want.

With SQL, you can insert, delete, and update data and create, delete, or alter other database objects. The standard SQL commands are “select”, “delete”, “insert”, “update”, “create”, and “drop”. These can accomplish everything that one needs to do on a database.

Moreover, this language is used in multiple databases to help handle data and database objects. If it sounds complicated for you, here’s a video explaining what SQL is for beginners:

Can a database run without a language?

Why Do We Use SQL?

It’s pretty simple. We won’t understand databases without SQL. In the same way, we can’t instruct the database without it because SQL is a system used to communicate with a database.

SQL systems perform tasks such as deleting, adding, or altering data. This system is commonly used to make it easier to handle large amounts of data by efficiently managing it. A few standard relational database management systems that use SQL include Oracle, Sybase, Microsoft Access, and Ingres.

What’s Inner Join and Outer Join?

Well, firstly, let’s understand what joins are. In SQL, joins are used to combine the contents of different tables. You can combine the data in many ways by specifying how you want the data integrated and which type of Join you wish to use.

An Inner Join is a join that returns all rows from both the participating tables where the essential record of one table is the same as the critical records of another table. 

This sort of Join required a comparison operator to match rows from the participating tables that supported a standard field or column of both the tables.

Outer Join can return non-matching rows in one or both of the tables. Basically, it returns all rows from all the tables which meet the conditions.

There are many different types of Outer Joins. These include Left Join, Right Join, and Full Outer Join.

Here’s a table summarizing the significant functions of the joins available in SQL:

Types of Joins:Function:
Inner Join This returns rows when there is at least one match in both tables.
Left Outer Join This returns all the rows from the left table in conjunction with the matching rows from the right table.
Right Outer Join This returns all the rows from the right table in conjunction with the matching rows from the left table.
Full Outer JoinThis combines left outer Join and right outer Join. Returns rows from either table when conditions are met.
This shows the differences between four Joins in SQL.

Difference Between Inner and Outer Join

There’s more. The significant difference between the inner and outer joins is that inner joins usually result in the intersection of two tables. In contrast, Outer Joins result in the mixing of two tables.

So basically, Inner Join results in the overlapping part of two data sets, as shown in the picture below. You will combine only those standard rows in both tables for Inner Joins. On the other hand, Outer Joins returns all the records with values in either left or suitable tables.

Outer joins include the matching rows and the non-matching rows from the tables. Moreover, an Outer Join differs from an inner join in managing the false match condition.

Left Outer Join consists of Left Outer Join + Inner Join. While the Right Outer Join is also consist of consists of Right Outer Join + Inner Join. Full Outer Join consists of them all.

Left Join (Is it the Same as Left Outer Join in SQL?)

Perhaps you might have heard of Left Join in SQL too? Well, it’s just the same Left Outer Join. They have two different names for the same function.

A left join is the same as a Left outer join in SQL, and they are one. The Left Join is just a shorthand for the left outer Join. The word “outer” just makes it more straightforward what the operation is, but both keys perform the same functions.

Why Left Join is Called the Left Outer Join?

You’ll have options to call it by its extended name or the shortcut one. Besides, they’re just the same thing.

Remember that this Join returns all the rows in the table on the left side and the matching rows on the right side of the Join. If there are no matching sides on the right side, the result is null.

So if we were to join two tables, A and B, SQL Left Outer Join would return all rows in the left table, which is A, and all of the rows that match in the other table B on the right side. In short, the result of the SQL Left Join always consists of the rows from the left side table.

Difference Between Join and Left Join

For the basics, Join is also called an Inner Join, while Left Join is an Outer Join.

But the main difference is that a left join statement is likely to include and combine all rows of the table referenced on the left side of the information. Instead of just the unmatched rows, it consists of all rows from the left table and matched rows from the other tables.

When to use Left Outer Join in SQL?

Suppose you’re looking for a way of combining different tables. Or, if you are joining two tables and want the result set to include only one table’s unmatched rows, you should use a left outer join clause or a proper outer join clause. Using Left Outer Join consists of the rows that don’t match from the table specified before the left outer join clause.

Technically, the left outer Join identifies all the rows from both the tables that meet the join condition and unmatched rows from the table.

Does Left Outer Join Increase the Number of Rows?

This is a frequently asked question. Technically, it’s a yes.

However, Left Join can only increase the number of rows in the left table. And this is only when multiple matches are in the right table. In addition, you can use numerous Left Joins in one query if it is needed for your analysis.

Left Outer Join vs. Right Outer Join

The significant difference between the Left Outer Join and the right outer Join is combining non-matched rows.

So the difference between the two is that the left outer Join includes the unmatched rows or all records of the table at the Left of the join clause, including the matched rows from the right table or clause.

On the other hand, a Right outer join includes unmatched rows from the table on the right side of the Join clause and returns all rows from the right side.

A Join clause combines records or modifies and manipulates forms from two or more tables using a join condition. This Join condition indicates how the columns from the different tables are matched when compared.

For instance, there will be a standard column between a table containing employee salary and another table containing employee details. This could be employee ID, and this helps Join the two tables.

So you can think of the table as an entity, and the key is a common link between the two tables, which is used for joint operation.

A person working on his laptop.
Studying Databases can be tricky. But it’s pretty simple to get if you understand it thoroughly.

What’s the Difference Between Right Join and Right Outer Join?

Right joins are similar to left joins, except they return all rows in the table from the right side and matching ones from the Left.

Again, the Right Join and Right Outer Join have no specific difference, the same way a Left Join and Left Outer Join don’t. In short, the term Right Join is simply a shorthand for Right Outer Join.

The “outer” keyword is optional. They both perform the same job, combining the datasets and tables.

Why Use Right Join Instead of Left Join?

Generally, the Right Outer Joins are not used as commonly because you can always replace them with Left Outer Joins, and one wouldn’t have to perform any additional functions.

One would think about using Right Join rather than Left Join when trying to make your SQL more self-documenting.

You might use the Left Join to address queries that have null rows on the dependent side. You would use Right Join for questions that generate null rows on the independent side.

The Right Outer Join is also helpful when you need to combine one table with the intersection of many other tables.

Difference Between Join and Union in SQL

The difference between Join and Union is that Union is used to combine the result set of two or more SELECT statements.

While Join combines data from many tables depending on the matched condition, data combined using Join statements results in new columns.

The data combined using the Union statement results in new distinct rows from the sets with an equal number of columns.

Final Thoughts

In conclusion, there’s no difference between LEFT JOIN and LEFT OUTER JOIN. This is also true for Right Join and Right Outer Join.

Both the keys perform the same functions, and “outer” is just an optional keyword to use. Some people recommend using it only because it clarifies that you’re creating an Outer Join.

So, in the end, whether you specify it or not makes no difference at all.

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Click here to learn more about these differences in a more summarized manner.