--- or 

The standard boolean operator `or' can be used to connect simple
   boolean expressions to form more complex expressions.

Square brackets are used to indicate which part of the expression
  will be evaluated first.

EXAMPLE:

	  sql> where salary > 2000 or job = 'enginner'

	  sql> where [job = 'clerk*' and dept_no = 10] or
		     [job = 'programmer*' and dept_no = 60]

