dbQuoteLiteral() 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.

When passing the returned object again to dbQuoteLiteral() 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.)


The returned expression can be used in a SELECT ... query, and the value of dbGetQuery(paste0("SELECT ", dbQuoteLiteral(x)))[[1]] must be equal to x for any scalar integer, numeric, string, and logical. If x is NA, the result must merely satisfy is.na(). The literals "NA" or "NULL" are not treated specially.

NA should be translated to an unquoted SQL NULL, so that the query SELECT * FROM (SELECT 1) a WHERE ... IS NULL returns one row.

Passing a list for the x argument raises an error.