Tables in a relational database are linked together via foreign keys. To extract data from linked tables, we utilised the JOIN clause.

The join condition specifies how each table's columns are compared.

INNER JOIN and OUTSIDE JOIN are the two types of JOIN clauses in SQL.

The OUTSIDE JOIN is broken down into sections once more.

  1. LEFT OUTER JOIN - This join returns all data from the left table as well as records from both tables that are matched.
  2. RIGHT OUTER JOIN - returns all data from the right table as well as records from both tables that are matched.


Only the information from the two connected tables that is related will be kept in the INNER JOIN.

An inner join is a query that returns joined tuples from two or more tables where at least one attribute is shared. It will return nil if there are no attributes in common across tables.

Example: Let's start by using JOIN.

You'd SELECT the column name from the pets table (and rename it pet name) in this example.

Then you'd go into the owners table and rename the name column owner. This is what it would look like: SELECT pet name from pets.name and owner.name from owners.name.

You'd use FROM to indicate that the columns come from the pets table, and JOIN to indicate that you want to join it with the owners table. JOIN the owner from the pets.

Finally, when the owner id field in the pets table equals the id column in the owner table, you would use ON pets.owner id = owners.id to combine two rows together.

ON CO_Customer.CID=CO_Order.CID;


In SQL, it's a form of JOIN operation. Even if the join condition fails, an outer join returns the merged tuples from a given table. In SQL, there are three types of outer joins:

Join the left outer ring, the right outer ring, and the full outer ring.

LEFT JOIN is the most widely used join type in all SQL versions. However, this is not the case for the RIGHT JOIN and FULL JOIN , which are not supported by all SQL versions .

Example 1: SQL LEFT JOIN example

To see the difference, run the same query using LEFT JOIN. The query is identical except for the addition of the LEFT keyword.

SELECT Customer.CustName, Product.PrdtName
  FROM Customer
  LEFT JOIN Product
  ON Customer.ID = Product.ID;

The rows from the left table, Customer, are all retained in this situation, and when data from the owners table is missing, it is filled with NULL.

CustName PrdtName
john Cookies
olly Layz
NULL Chocolates

Example 2: SQL RIGHT JOIN example

If you run the same query with the RIGHT JOIN operator, you'll get a different result.

SELECT Customer.CustName, Product.PrdtName
  FROM Customer
  RIGHT JOIN Product
  ON Customer.ID = Product.ID;

All rows from the right table, owners, are maintained in this situation, and any missing values are filled with NULL

Output: The output of above query is

CustName PrdtName
john Cookies
olly Layz
NULL Chocolates

There appears to be an Customer who does not have a Product Order.

Example 3: SQL FULL JOIN example

You could do the same query again, using FULL JOIN.

SELECT Customer.CustName, Product.PrdtName
  FROM Customer
  FULL JOIN Product
  ON Customer.ID = Product.ID;


There are 13 main distinguish in inner join & outer join in below table:-

Inner joins only operate when a matching condition exists. If any column in both tables matches, the entries will be combined using an inner join. When there are no matching columns, an outer join is used to combine the entries. In this situation, the outer join joins all of the column's entries together.
An inner join removes the column and returns the result without it. Take into account Diagram of a Venn diagram The result of joining two tables is known as an outside join.
If two tables are included in a Venn diagram, the inner join is the intersection of A and B. If two tables A and B are taken into account. The union of A and B is the outside join.
INNER JOIN and JOIN clauses were used. There are three types of outside joins: left outer join, right outer join, and full outer join. The left outside join joins the tables on the left side, the right outer join joins the entries from the right table, and the whole outer join joins all of the tables together.
For an inner join, a record with a relevant ID must exist in the resultant table. This displays the output along with the relevant data. The linked ID is not required for an outer join. The output of an outer join is such that the complete table is visible for a full join. As a result, the final outcome is greater.
If the records do not match, the entry is not included in the inner join result. In Outer Join, if the records in the tables do not match, the value is returned as null.
From the tables, there should be at least one common entry for inner join. Common entries are not required for outer joins, although they should not be avoided if they exist.
For both inner and outer joins, a query is written. In an inner join, the query specifies that two tables should be matched based on the query, and if the rows from the first table match the rows from the second table, the rows from the second table should be printed. In an outer join, the query defines the rows of two tables, and if the two tables don't match, both tables are returned as output. If the table contains a match, all entries, including the common entry, are returned as output.
If the number of tuples is greater than one. Then the INNER JOIN is more efficient than the OUTER JOIN. The OUTER JOIN is generally slower than the INNER JOIN. However, there are a few exceptions.
The optimizer can be employed because it provides a lot of useful options. The use of the optimizer in the outer join is quite limited because the joins require all of the entries, making its use impractical.
The inner join condition must be met in order to proceed. In the outer join query, we don't have to meet any requirements at all.
It is a simple method in which the matching values for left and right tables should not be evaluated. In an outer join, if the entries match, it will verify whether a condition is specified for the left or right tables, and the entry will be treated as such, with the exception of a full outer join.
The inner join is advised if a related data entry is required due to a client demand or database design. If a related data entry isn't required by the client or the database design, the outer join is the better option.