SQL
SQL quoting
This set of classes and generics make it possible to flexibly deal with SQL
escaping needs. By default, any user supplied input to a query should be
escaped using either dbQuoteIdentifier or dbQuoteString
depending on whether it refers to a table or variable name, or is a literal
string.
These functions return an object of the SQL class,
which tells DBI functions that a character string does not need to be escaped
anymore, to prevent double escaping.
The SQL class has associated the SQL() constructor function.
Usage
SQL(x)
dbQuoteIdentifier(conn, x, ...)
dbQuoteString(conn, x, ...)Arguments
- x
- A character vector to label as being escaped SQL.
- conn
- A subclass of
DBIConnection, representing an active connection to an DBMS. - ...
- Other arguments passed on to methods. Not otherwise used.
Value
-
An object of class
SQL.
Implementation notes
DBI provides default generics for SQL-92 compatible quoting. If the database
uses a different convention, you will need to provide your own methods.
Note that because of the way that S4 dispatch finds methods and because
SQL inherits from character, if you implement (e.g.) a method for
dbQuoteString(MyConnection, character), you will also need to
implement dbQuoteString(MyConnection, SQL) - this should simply
return x unchanged. If you implement your own method, make sure to convert NA to NULL (unquoted).
See Also
Other DBIResult generics: DBIResult-class,
dbBind, dbClearResult,
dbColumnInfo, dbFetch,
dbGetInfo, dbGetRowCount,
dbGetRowsAffected,
dbGetStatement,
dbHasCompleted, dbIsValid
Other DBIResult generics: DBIResult-class,
dbBind, dbClearResult,
dbColumnInfo, dbFetch,
dbGetInfo, dbGetRowCount,
dbGetRowsAffected,
dbGetStatement,
dbHasCompleted, dbIsValid
Examples
library(DBI)
# Quoting ensures that arbitrary input is safe for use in a query
name <- "Robert'); DROP TABLE Students;--"
dbQuoteString(ANSI(), name)
dbQuoteIdentifier(ANSI(), name)
# NAs become NULL
dbQuoteString(ANSI(), c("x", NA))
# SQL vectors are always passed through as is
var_name <- SQL("select")
var_name
dbQuoteIdentifier(ANSI(), var_name)
dbQuoteString(ANSI(), var_name)
# This mechanism is used to prevent double escaping
dbQuoteString(ANSI(), dbQuoteString(ANSI(), name))