Comments is used to add a line which is not executed in the output.
Single line Comments
It starts with - -
- - Select all the employee
SELECT * FROM employee;
SELECT * FROM employee - - WHERE salary = 50,000 ;
In this example, the details of all the employee will be generated , not the salary. Here the salary is commented.
Multiple line comments starts with / * */ .
Any thing you write between the commented line it will not be considered ( ignored ).
/ * This will not be considered * /
/ * SELECT * FROM employee ;
SELECT * FROM student ; * /
SELECT * FROM library ;
In this example, employee and student is commented, so details of library will be generated or fetched.