In SQL, the left join is a type of join operation that returns all records from the left table, and then matches any remaining records from the right table. The left outer join is similar to the left join, but it also includes unmatched records from the right table. In this article, we’ll take a look at the differences between these two types of joins.
What is Left Join?
Left Join is a type of join that returns all rows from the left table, even if there are no matches in the right table. Left Join is also known as Left Outer Join. Left Join is different from Inner Join, which only returns rows that have matches in both tables. Left Join is also different from Right Join, which is the reverse of Left Join and returns all rows from the right table, even if there are no matches in the left table.
Left Join can be used to find missing values in a data set by joining it with another data set that contains those values. Left Join can also be used to combine data sets where one data set has more observations than the other. In general, Left Join should be used whenever you want to keep all of the observations from one data set and add additional information from another data set.
What is Left Outer Join?
- Left Outer Join is a type of join that returns all the rows from the left table, even if there are no matches in the right table. It effectively Left Joins the two tables together and then uses a WHERE clause to filter out any results that don’t match in the second table. Left Outer Joins are useful when you want to make sure that all the rows from the first table are included in the results, even if there are no matches in the second table.
- For example, if you Left Outer Join a customer table with an order table, you would still see all the customers in the results, even if they had no orders. Left Outer Joins can also be used to fill in missing values.
- For example, if you Left Outer Join a table of employees with a table of departments, any employees who are not assigned to a department will have NULL values for the department columns. Left Outer Joins are typically used when it’s more important to include all the rows from the first table than it is to get accurate results.
Difference between Left Join and Left Outer Join
Left Join returns all the rows from the Left table and matching rows from the Right table. Left Outer Join returns all the rows from the Left table and all the matching rows from the Right table. Left Join will return only those records where the Left table’s field is equal to the Right table’s field. Left Outer Join will return all records from the Left table whether it is matched with the Right table or not. If the Left table has no match in the Right table, then Left Join will not return those rows whereas Left Outer Join will return those rows with NULL values in the fields of the Right table. In short, Left Join includes NULL values also but Left Outer Join excludes NULL values. So, we can say that Left Outer Join is a subset of Left Join.
Conclusion
In this blog post, we’ve outlined the differences between Left Join and Left Outer Join. We hope that this information has been helpful in clarifying these two joins for you.
