Updating a column of a table

Hi all

I have a problem in updating one column in the target table(say table A) from a column in the source table (say table B).

All the columns in table A has been populated. Just one column should be populated. My source is a SQL object that contains a complex sql query that returns three columns date_from, date_to and ID.

In the table A, I have the same date_from and date_to and need to get the ID from the SQL object and set it to the corresponding ID in the table A.

I tried many ways to update the table, but it I couldn't ;(

I should read from a table and update it based on a look-up function mapped to the column I need to update.

I want to map the ID colmn from table A to a look-up ext function that can get the column from the table B. However I don't know how to use the Data Services objects to just update 1 column. If you could give me a consequence of the DS objects to be update a table based on a look-up , I would be so grateful.

Thanks.