Pentaho Kettle weird Left Join results

Question

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.

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Answer 1

Regarding "merge join" step:

Note: In this step rows are expected to be sorted on the specified key fields.

(source)

Answer 2

I believe that you can be using a join without adding the Sort step, otherwise unexpected results might come out.

See what the kettle documentation.

Pentaho Documentation ** PRINT show: Docs Pentaho about JOINs**

Whenever you use a JOIN in Pentaho add a Step Sort with the join IDs so that the pentaho can sort the results before joining, so you'll be able to sort without any problems.

Print - Example JOIN with SORT