I am using kettle too make a left join between two tables who share common keys, however despite in some rare cases the join works as I intended, in most of them it returns NULL despite sharing the same key as in the cases where it works. Like in the example bellow.
EDIT: In one table I have ID_DOENTE and ID_TIPO_CONSULTA, while in other I have TIPO_CONSULTA and ID_TIPO_CONSULTA. I am merging the first table using left join with the 2nd using ID_TIPO_CONSULTA as the key. The result is the following
As you can see the in the rows with ID_DOENTE 40, the join works in a single case, but for all the other rows despite the situation being identical it leaves the values coming from the 2nd table as NULL.
Regarding "merge join" step:
Note: In this step rows are expected to be sorted on the specified key fields.