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 About the Firebird 5.0 Language ReferenceData Types and Subtypes 

Literals

Literals are used to directly represent values in a statement.Examples of standard types of literals are:

integer        - 0, -34, 45, 0X080000000;
fixed-point    - 0.0, -3.14
floating-point - 3.23e-23;
string         - 'text', 'don''t!', Q'{don't!}';
binary string  - x'48656C6C6F20776F726C64'
date           - DATE '2018-01-19';
time           - TIME '15:12:56';
timestamp      - TIMESTAMP '2018-01-19 13:32:02';
boolean        - true, false, unknown
null state     - null

Details about literals for each data type are discussed in section Literals (Constants) of chapter Common Language Elements.

Operators and Special Characters

A set of special characters is reserved for use as operators or separators.

<special char> ::=
  any of <space> or "%&'()*+,-./:;<=>?|^{}

Some of these characters, alone or in combination, may be used as operators (arithmetical, string, logical), as SQL command separators, to quote identifiers, or to mark the limits of string literals or comments.

Operator Syntax
<operator> ::=
    <string concatenation operator>
  | <arithmetic operator>
  | <comparison operator>
  | <logical operator>

<string concatentation operator> ::= '||'

<arithmetic operator> ::= * | / | + | -

<comparison operator> ::=
    =  | <> | != | ~= | ^= | > | < | >= | <=
  | !> | ~> | ^> | !< | ~< | ^<

<logical operator> ::= NOT | AND | OR

For more details on operators, see Expressions.