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 Data Types and SubtypesData Definition (DDL) Statements 

Literals (Constants)

A literal — or constant — is a value that is supplied directly in an SQL statement, not derived from an expression, a parameter, a column reference nor a variable.It can be a string or a number.

String Literals

A string literal is a series of characters enclosed between a pair of apostrophes (“single quotes”).The maximum length of a string literal is 32,765 for CHAR/VARCHAR, or 65,533 bytes for BLOB;the maximum character count will be determined by the number of bytes used to encode each character.

Formally, the syntax of a normal string literal is:

Character String Literal Syntax
<char-literal> ::=
  [<introducer> charset-name] <quote> [<char>...] <quote>
  [{ <separator> <quote> [<char>...] <quote> }... ]

<separator> ::=
  { <comment> | <white space> }

<introducer> ::= underscore (U+005F)
<quote> ::= apostrophe (U+0027)
<char> ::= character representation;
           apostrophe is escaped by doubling
Note

  • Double quotes are not valid for quoting strings.The SQL standard reserves double quotes for a different purpose: delimiting or quoting identifiers.

  • If a literal apostrophe is required within a string constant, it is “escaped” by prefixing it with another apostrophe.For example, 'Mother O''Reilly''s home-made hooch'.Or use the alternative quote literal: q'{Mother O'Reilly's home-made hooch}'

  • Care should be taken with the string length if the value is to be written to a CHAR or VARCHAR column.The maximum length for a CHAR or VARCHAR literal is 32,765 bytes.

The character set of a string constant is assumed to be the same as the character set of its destined storage.

Examples
-- Literal containing single quote
select 'O''Reilly' from RDB$DATABASE;
-- output: O'Reilly
-- whitespace between literal
select 'ab'
       'cd'
from RDB$DATABASE;
-- output: abcd
-- comment and whitespace between literal
select 'ab' /* comment */ 'cd'
from RDB$DATABASE;
-- output: abcd