Explicit v/s. Implicit SQL Joins

The explicit join is easier to read and the implicit syntax is difficult to understand and more prone to errors. Moreover implicit syntax is now a day’s outdated.

 SQL specifies two different syntactical ways to express joins: "explicit join notation" and "implicit join notation":

 The "explicit join notation" uses the JOIN keyword to specify the table to join, and the ON keyword to specify the predicates for the join, as in the following example:

SELECT *

FROM employee INNER JOIN department

ON employee.DepartmentID = department.DepartmentID;

The "implicit join notation" simply lists the tables for joining (in the FROM clause of the SELECT statement), using commas to separate them. Thus, it specifies a cross-join, and the WHERE clause may apply additional filter-predicates (which function comparably to the join-predicates in the explicit notation).

 The following example shows a query which is equivalent to the one from the previous example, but this time written using the implicit join notation:

SELECT * 

FROM   employee, department

WHERE  employee.DepartmentID = department.DepartmentID;

 [Via]