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.