Select x.X1, x.X2, y.X3
into z
from x inner join y on x.X1 = y.X1

x<-data.frame(cbind('X1'=c(5,9,7,6,4,8,3,1,10,2),'X2'=c(5,9,7,6,4,8,3,1,10,2)^2))
y<-data.frame(cbind('X1'=c(9,5,8,2),'X3'=c('nine','five','eight','two')))

z<-cbind(x[which(x$X1 %in% (y$X1)), c(1:2)][order(x[which(x$X1 %in% (y$X1)), c(1:2)]$X1),],y[order(y$X1),2])

library(sqldf)
 z <- sqldf("SELECT X1, X2, X3 FROM x JOIN y
      USING(X1)")