A literal is an unknown data object that is defined fully by virtue of its value (specifies a non-NULL value, see data type). Literal values cannot be modified. A distinction is made between string literals and numeric literals.
<literal> ::= <string_literal> | <numeric_literal>
string_literal, numeric_literal
String literals
'69190 Walldorf'
'Anthony Smith'
Numeric literals
+0.58498
1E160
-765E-04