Tài liệu PL/SQL User’s Guide and Reference phần 9

Two kinds of numeric literals can be used in arithmetic expressions: integers and
reals. Numeric literals must be separated by punctuation. Spaces can be used in
addition to the punctuation.
A character literal is an individual character enclosed by single quotes
(apostrophes). Character literals include all the printable characters in the PL/SQL
character set: letters, numerals, spaces, and special symbols.
PL/SQL is case sensitive within character literals. So, for example, PL/SQL
considers the literals ’Q’ and ’q’ to be different.