SQL LEFT JOIN

The SQL Left Join is a Join used to return all the records (or rows) present in the Left table and matching rows from the right table.

NOTE: All the Unmatched rows from the right table will be filled with NULL Values.

SQL LEFT JOIN Syntax

The basic syntax of the Left Join in SQL Server is as follows:

TIP: In SQL Server, Left Outer join can also be called as Left Join so it is optional to use the Outer Keyword.

Let us see the visual representation of the Left Outer join for better understanding.

From the above image you can understand easily that, Left Outer join displays all the records present in Table 1 and matching records from Table 2

In this article we will show you, How to write Left Join in SQL Server 2014. For this, We are going to use two tables (Employee and Department) present in our [SQL Server Tutorials] Database.

Data present in the Employee Table is:

Data present in the Department Table is:

SQL Left Join – Selecting All Columns

The following SQL Query will display all the columns present in Employees and Department tables

T-SQL CODE

OUTPUT

If you observe the above screenshot, We have 15 records in Employee table, Left Outer Join is displaying 15 records but for [DepartID], id, [Department Name] it is displaying NULL Values for the ID number 10, 11, 14 and 15 . This is because, Department Id for them in Employee table are NULLS so there is no matching records in right table.

NOTE: The [Department ID] column is repeated twice, which is annoying to the user. By selecting individual column names we can avoid unwanted columns so, Please avoid SELECT * Statements in Left Join

SQL Left Join – Selecting Few Columns

Please place the required columns after the SELECT Statement to avoid unwanted columns

T-SQL CODE

OUTPUT

Above query will perfectly work as long as the column names from both tables (Employee and Department) are different like above. What happens if we have same Column names in both the tables? Well, you will end up in a mess. Let us see how to resolve the issue.

The following query is using table name before the column name and also used the ALIAS names to rename the column names. By this approach we can inform the Database that we are looking for columns belonging to particular table.

T-SQL CODE

OUTPUT

Although we don’t have any common column names, Imagine we have [DepartmentName] column in Employee as well and we want to display Department Columns in both the tables.

We can simply write as

NOTE: It is always best practice to use the table name before the Column name in Joins. For example, SELECT Employee.Firstname

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