spec_sql_unquote_identifier

## Value

dbUnquoteIdentifier() returns a list of objects of the same length as the input. For an empty character vector this function returns a length-0 object. The names of the input argument are preserved in the output. When passing the first element of a returned object again to dbUnquoteIdentifier() as x argument, it is returned unchanged (but wrapped in a list). Passing objects of class Id should also return them unchanged (but wrapped in a list). (For backends it may be most convenient to return Id objects to achieve this behavior, but this is not required.)

An error is raised if plain character vectors are passed as the x argument.

## Specification

For any character vector of length one, quoting (with dbQuoteIdentifier()) then unquoting then quoting the first element is identical to just quoting. This is also true for strings that contain special characters such as a space, a dot, a comma, or quotes used to mark strings or identifiers, if the database supports this.

Unquoting simple strings (consisting of only letters) wrapped with SQL() and then quoting gives the same result as just quoting.