X<-data.frame(table1=c("col1","col2"),types1=c("int","char(4)"))
 Y<-data.frame(table2=c("col2","col3"),types2=c("char(8)","tinyint"))

table1   types1   types2
    col1     int      NA
    col2     char(4)  char(8)
    col3     NA       tinyint

table1   table2   types1   types2
    col1     NA       int      NA
    col2     col2     char(4)  char(8)
    NA       col3     NA       tinyint