A literal (literal) is an unknown data object that is defined fully by virtue of its value (specifies a non-NULL value). You cannot change the value of a literal. A distinction is made between string literals and numeric literals.
<literal> ::= <numeric_literal>
<string_literal> ::= ''
<hex_literal> ::= x''
<hex_digit_seq> ::= <hex_digit><hex_digit>
<hex_digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9
| A | B | C | D | E | F
| a | b | c | d | e | f
A numeric literal (numeric_literal) is a number represented as a fixed or floating point number.
A string literal (string_literal) is a sequence of characters in quotation marks. String literals can also be represented in hexadecimal notation by preceding them with x or X.
An apostrophe within a character string is represented by two successive apostrophes.
A string literal of the type '<character>...' or '' is only valid for a value referring to an alphanumeric column with the code attribute ASCII.
A hexadecimal value (hex_literal) is only valid for a value referring to a column with the code attribute BYTE.
A string literal of the type '', x'', and X'' , and string literals that only contain blanks are not the same as the NULL value.