One of the best languages for managing data is SQL. This language is often used for database management and other related tasks.
However, if you’re not familiar with SQL and how to use it, you may feel confused when you hear about certain terms, such as outer joins, SQL inner join, or outer join returns.
Today, we’re going to cover everything you need to know about inner join in SQL so that you can understand what it is, and how to use it to your advantage.
We’re going to take a look at SQL inner joins in more detail so that you can become proficient in this computer language and use it to your advantage.
Let’s take a look at everything you need to know about SQL inner joins down below.
What Is Inner Join In SQL?
Inner joins are one of the most common operations performed on relational databases. They allow us to combine two tables together based on some matching criteria.
The result of an inner join will be all records from both tables that match the specified conditions.
For example, let’s say we have a table called “customers” and another table called “orders”. If we want to find out which customers placed orders, we could do something like:
SELECT * FROM Customers INNER JOIN Orders ON Customers.CustomerID Orders.CustomerID;
This query would return every customer who has ever made an order.
The first thing to note here is that there must be a relationship between the two tables. In our case, we’ve joined them using CustomerID.
It’s important to remember that this means that each record in the Customers table must also exist in the Orders table.
If we wanted to only show customers who had never ordered anything, we’d change the condition to WHERE Customers.CustomerID IS NULL.
What Is The Difference Between Inner Join And Outer Join In SQL?
The difference between SQL inner join and outer joins is simple – they work differently. An inner join combines the rows from both tables into one set while an outer join keeps the original sets separate.
To illustrate this, imagine that we have a list of people (the Customers table) and their favorite food (the Orders table). We might want to see all of the people who haven’t ordered any food yet.
For this purpose, we’ll use an outer join. Here’s what we’d write:
SELECT * FROM Customers OUTER JOIN Orders ON Customers.CustomerID Orders.CustomerID;
Notice that we didn’t specify any conditions in the WHERE clause because we don’t care whether the person has already ordered anything. All we want is to see all of the customers.
Now, let’s say that we want to see everyone who hasn’t ordered anything, but we also want to include those who have ordered food before. To do this, we’ll use an inner join instead.
Here’s what we’ll type:
SELECT * FROM Customers INNER Join Orders ON Customers.CustomerId Orders.CustomerID;
Notice that we added the word “inner” after the keyword “join”, indicating that we want to perform an inner join.
This is why we get different results when we use these two types of joins.
What Are The Three Types Of Joins In SQL?
There are lots of different types of joins in SQL. Let’s go over the different types of joins in SQL so that we can understand them all a bit better.
These are the simplest types of joins. Basically, they just bring together rows from two tables where the values match.
For instance, if we were looking for all customers who have never ordered anything, we could simply write: SELECT * FROM Customers LEFT OUTER JOIN Orders ON Customers.CustomerID Orders.CustomerID WHERE Orders.OrderDate IS NULL.
Left Outer Join
A left outer join combines the results of the right side of a join with those of the left side.
So, if we were trying to get all customers who have never made any orders, we could write: SELECT * FROM Orders RIGHT OUTER JOIN Customers ON Orders.CustomerID Customers.CustomerID WHERE Orders. IS NULL.
Right Outer Join
A right outer join combines the results from the right side of a query with those of the left.
So, if we wanted to get all customers who haven’t made any orders, we’d write: SELECT * FROM Order RIGHT OUTER JOIN Customer ON Orders.CustomerID Customer.CustomerID WHERE Orders IS NULL.
Full Outer Join
A full outer join combines the results in two different ways.
First, it combines the results of the left side of the join with those of the right side.
Second, it combines the results from the left side of the query with those of the right.
So, if we needed to find all customers who have not yet made any orders, we might write: SELECT * FROM Customer FULL OUTER JOIN Orders ORDER BY Customer.CustomerID DESC.
This would give us all customers who haven’t yet made any orders, but it wouldn’t give us any information about their orders.
To see what they’ve ordered, we’d have to add a second join: SELECT * FROM Customer FULL OUTER JOIN Orders USING (CustomerID) ORDER BY Customer.CustomerId DESC.
When Should You Use Left Join Or Inner Join?
You should always use left join and inner join unless there’s a reason not to. There are times when using one of the other types of joins makes sense.
However, most of the time, you should stick with left join and inner join.
So there you have it! SQL inner join is simply the method that we use to combine records from two tables based on the fact that they share some common value.
You’ll often hear people refer to inner join as “inner plus”.
Inner join can be used in SQL to perform many different tasks.
We’ve looked at how to select all customers who have never placed an order, and we’ve seen that we can do this by joining the two tables using customer ID.
But we can also use inner join to select all customers who don’t have a particular attribute, such as name.
In this case, we’re selecting all customers who have no first names.
We can achieve this by writing: SELECT * FROM Customers INNER JOIN Names ON Names.FirstName Customers
So using SQL inner join can be a very efficient method to find matching rows of data in your database.
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