Tip: Use capital letters for AND, OR, NOT. Not all databases require it, but some do.
Boolean statements may be combined into a single search string. Parentheses are used to "nest" one Boolean expression within another and thereby govern the order in which the operations take place. In the following example,
sports AND injuries OR accidents
(sports AND injuries) OR accidents
the expressions are identical: "sports" AND "injuries" are combined first, and the resulting set is combined with "accidents". In each case the number of documents in the result list is the same.
In the expression
(injuries OR accidents) AND sports
the words within the parentheses, "injuries" and "accidents," are combined using the operator OR, and then combined with "sports" using AND. The expression
sports AND (injuries OR accidents)
is equivalent, and would find the same number of documents as number 3.
(sports and injuries) OR (sports AND accidents)
is equivalent to the searches in box 2, because all the articles must contain the key word "sports." In the first two expressions, only the articles which contain the word "injuries" must contain "sports". The list resulting from number 1 (or number 2) also contains all the articles including the word "accidents," whether or not "sports" appears.