why there are missing values and “0” in the variable"ftotval"?

There shouldn’t be any missing values in the FTOTVAL variable within ASEC samples. In basic monthly samples, however, the FTOTVAL variable will be coded as “missing”, because this variable is only available in ASEC samples. After looking at several of your most recent data extracts, it looks like you are including both ASEC and basic monthly samples within the same abstract. So, my guess is that the values that you see as “missing” are associated with non-ASEC sample records. If not, let us know.

Regarding codes of “0”: this indicates that a family has reported zero income.