SQL keywords are not case-sensitive that means 'SELECT' is same as 'select'. But the database name, table name, field name may be case-sensitive depending on the operating system. In general, Unix or Linux platforms are case-sensitive, whereas Windows platforms aren't.
SELECT emp_name, salary FROM employees;
The above statement can also be written, as follow:
select emp_name, salary from employees;
Tip: It is recommended to write the SQL keywords in uppercase, to differentiate it from other text inside a SQL statement for a better understanding.
A comment is simply a text that is ignored by the database engine. Comments can be used to provide a quick hint about the SQL statement.
SQL support single-line as well as multi-line comments. To write a single-line comment start the line with two consecutive hyphens (--). For example:
-- Select all the employees SELECT * FROM employees;
However to write multi-line comments, start the comment with a forward slash followed by an asterisk (/*) and end the comment with an asterisk followed by a forward slash (*/), like this:
/* Select all the employees whose salary is greater than 5000 */ SELECT * FROM employees WHERE salary > 5000;