SQL: retrieve only the records whose value has changed

Question

Sorry for the nondescript title. I\'ll edit as we go along.

I have a table RateTable:

| Code   |  Date     |   Rate  |

  B001     2009-         


        

Answer 1

If you add a new column "LastChangedDate" and you track the last read in an other table (ie. LastReadedValues), than you can easly track the changes.