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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 may 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.


SQL(x, ..., names = NULL)



A character vector to label as being escaped SQL.


Other arguments passed on to methods. Not otherwise used.


Names for the returned object, must have the same length as x.


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.


dbQuoteIdentifier(ANSI(), "SELECT")
dbQuoteString(ANSI(), "SELECT")

# SQL vectors are always passed through as is
var_name <- SQL("SELECT")

dbQuoteIdentifier(ANSI(), var_name)
dbQuoteString(ANSI(), var_name)

# This mechanism is used to prevent double escaping
dbQuoteString(ANSI(), dbQuoteString(ANSI(), "SELECT"))