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Alternative String Literals

It is possible to use a character, or character pair, other than the doubled (escaped) apostrophe, to embed a quoted string inside another string without the need to escape the quote.The keyword q or Q preceding a quoted string informs the parser that certain left-right pairs or pairs of identical characters within the string are the delimiters of the embedded string literal.

Syntax
<alternative string literal> ::=
    { q | Q } <quote> <start char> [<char> ...] <end char> <quote>
Note
Rules

When <start char> is ‘(’, ‘{’, ‘[’ or ‘<’, <end char> is paired up with its respective “partner”, viz. ‘)’, ‘}’, ‘]’ and ‘>’.In other cases, <end char> is the same as <start char>.

Inside the string, i.e. <char> items, single quotes can be used without escaping.Each quote will be part of the result string.
Examples
select q'{abc{def}ghi}' from rdb$database;        -- result: abc{def}ghi
select q'!That's a string!' from rdb$database;    -- result: That's a string
Introducer Syntax for String Literals

If necessary, a string literal may be preceded by a character set name, itself prefixed with an underscore “_”.This is known as introducer syntax.Its purpose is to inform the engine about how to interpret and store the incoming string.

Example

INSERT INTO People
VALUES (_ISO8859_1 'Hans-Jörg Schäfer')