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

Usage Notes
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.
A string literal is a sequence of zero or more characters enclosed by single quotes.
The null string (’’) contains zero characters. To represent an apostrophe within a
string, write two single quotes. PL/SQL is case sensitive within string literals. So,
for example, PL/SQL considers the literals ’white’ and ’White’ to be different.
Also, trailing blanks are significant within string literals, so ’abc’ and ’abc ’ are
different. Trailing blanks in a literal are never trimmed.
The Boolean values TRUE and FALSE cannot be inserted into a database column.