An Outer Join is a type of database join (commonly used in SQL) that returns records from one or both tables even if there’s no matching record in the other table.

Types of Outer Joins:

1. LEFT OUTER JOIN (or simply: LEFT JOIN):
   → Returns all records from the left table, and the matching ones from the right table.
   → If there’s no match, the result is filled with NULL values from the right table.

2. RIGHT OUTER JOIN (or: RIGHT JOIN):
   → Returns all records from the right table, and the matching ones from the left table.
   → If there’s no match, NULL is used for the left side.

3. FULL OUTER JOIN:
   → Returns all records from both tables, with NULL where no match exists on either side.

Example:

Suppose you have two tables:

• Customers

  CustomerID	Name
  1	Anna
  2	Bernd
  3	Clara

• Orders

  OrderID	CustomerID	Product
  101	2	Book
  102	4	Lamp

LEFT JOIN (Customers LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID)

An INNER JOIN is a term used in SQL (Structured Query Language) to combine rows from two (or more) tables based on a related column between them.

Example:

You have two tables:

Table: Customers

Table: Orders

Now you want to know which customers have placed orders. You only want the customers who exist in both tables.

SQL with INNER JOIN:

SELECT Customers.Name, Orders.Product
FROM Customers
INNER JOIN Orders ON Customers.CustomerID = Orders.CustomerID;

Result:

Explanation:

• Clara didn’t place any orders → not included.

• The order with CustomerID 4 doesn’t match any customer → also excluded.

In short:

An INNER JOIN returns only the rows with matching values in both tables.

An explicit join is a clear and direct way to define a join in an SQL query, where the type of join (such as INNER JOIN, LEFT JOIN, RIGHT JOIN, or FULL OUTER JOIN) is explicitly stated.

Example of an explicit join:

SELECT *
FROM customers
INNER JOIN orders
ON customers.customer_id = orders.customer_id;

This makes it clear:

• Which tables are being joined (customers, orders)

• What kind of join is used (INNER JOIN)

• What the join condition is (ON customers.customer_id = orders.customer_id)

In contrast: Implicit join

An implicit join is the older style, using a comma in the FROM clause, and putting the join condition in the WHERE clause:

SELECT *
FROM customers, orders
WHERE customers.customer_id = orders.customer_id;

This works the same, but it's less clear and not ideal for complex queries.

Benefits of explicit joins:

• More readable and structured, especially with multiple tables

• Clear separation of join conditions (ON) and filter conditions (WHERE)

• Recommended in modern SQL development

An implicit join is a way of joining tables in SQL without using the JOIN keyword explicitly. Instead, the join is expressed using the WHERE clause.

Example of an implicit join:

SELECT *
FROM customers, orders
WHERE customers.customer_id = orders.customer_id;

In this example, the tables customers and orders are joined using a condition in the WHERE clause.

In contrast, an explicit join looks like this:

SELECT *
FROM customers
JOIN orders ON customers.customer_id = orders.customer_id;

Differences:

When is an implicit join used?

It was common in older SQL code, but explicit joins are recommended today, as they are clearer, easier to maintain, and less error-prone, especially in complex queries involving multiple tables.