spec_sql_quote_identifier
dbQuoteIdentifier() returns an object that can be coerced to character,
of the same length as the input.
For an empty character vector this function returns a length-0 object.
An error is raised if the input contains NA,
but not for an empty string.
When passing the returned object again to dbQuoteIdentifier()
as x
argument, it is returned unchanged.
Passing objects of class SQL should also return them unchanged.
(For backends it may be most convenient to return SQL objects
to achieve this behavior, but this is not required.)
Calling dbGetQuery() for a query of the format SELECT 1 AS ...
returns a data frame with the identifier, unquoted, as column name.
Quoted identifiers can be used as table and column names in SQL queries,
in particular in queries like SELECT 1 AS ...
and SELECT * FROM (SELECT 1) ....
The method must use a quoting mechanism that is unambiguously different
from the quoting mechanism used for strings, so that a query like
SELECT ... FROM (SELECT 1 AS ...)
throws an error if the column names do not match.
The method can quote column names 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.
In any case, checking the validity of the identifier
should be performed only when executing a query,
and not by dbQuoteIdentifier().