Best Indexing for Performance - MySQL
The engine will only be able to make use of one index per table so while the other indexes may help you in the future with other queries, their benefit will be limited in assisting you with this particular query.

Given what we know about your query and limited knowledge of the table and the insert pattern, I would suggest the following.

Table A - (Date, Type)
Table B - (merk, ID, Code)
Table C - (Uniq)


Of course, if you were able to limit the result set columns (getting rid of the SELECT *) then further columns in the index could be of benefit.  

These indexes above will allow the engine to seek quickly and get quickly to the rows that it wants.  

I do have one question about the "merk" on Table B.  If that is something like a status that changes then I would not index on it, leaving just an index on ID and Code.  If the value of the field changes frequently then it is usually a poor index candidate as it will cause much fragmentation.