A string literal is a literal consisting of a sequence of characters enclosed in quotation marks. String literals can also be represented in hexadecimal notation by preceding them with x or X.
<string_literal> ::= '' | '<character>...' | <hex_literal>
'69190 Walldorf'
'Anthony Smith'
X'12ab'
A quotation mark within a character string is represented by two successive quotation marks.
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 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.