SQL Access Iif(aantal_instroom) as instroom - sql

Question

I've got this:
sql = "SELECT " & _
"proces_id, " & _
"proces_naam, " & _
"voorraad, " & _
"voorraad_te_laat, " & _
"voorraad_verificatie, " & _
"voorraad_verificatie_te_laat, " & _
"teamplanning, " & _
"teamplanning_verificatie, " & _
"Iif(IsNull(teamplanning_totaal), 0, teamplanning_totaal) + Iif(IsNull(teamplanning), 0, teamplanning) AS totaal_teamplanning, " & _
"Iif(IsNull(teamplanning_totaal_verificatie), 0, teamplanning_totaal_verificatie) + Iif(IsNull(teamplanning), 0, teamplanning_verificatie) AS totaal_teamplanning_verificatie, " & _
"Round(Iif(IsNull(teamplanning), 0, (teamplanning * proces_normtijd * Iif(IsNull(productiviteit_factor), 1, productiviteit_factor)) / 60), 2) AS teamplanning_uren, " & _
"Round(Iif(IsNull(teamplanning_verificatie), 0, (teamplanning_verificatie * proces_normtijd_verificatie * Iif(IsNull(productiviteit_factor), 1, productiviteit_factor)) / 60), 2) AS teamplanning_uren_verificatie, "
If IsNull(Datum) Then
sql = sql & "null AS verschil, " & _
"null AS verschil_verificatie, "
Else
sql = sql & "Iif(IsNull(voorraad), 0, voorraad) - Iif(IsNull(teamplanning), 0, teamplanning) - Iif(IsNull(teamplanning_totaal), 0, teamplanning_totaal) AS verschil, " & _
"Iif(IsNull(voorraad_verificatie), 0, voorraad_verificatie) - Iif(IsNull(teamplanning_verificatie), 0, teamplanning_verificatie) - Iif(IsNull(teamplanning_totaal_verificatie), 0, teamplanning_totaal_verificatie) AS verschil_verificatie, "
End If
sql = sql & "proces_normtijd, " & _
"proces_normtijd_verificatie, " & _
"Iif(IsNull(realisatie_cases), 0, realisatie_cases) AS realisatie_cases_aantal, " & _
"Iif(IsNull(realisatie_cases_verificatie), 0, realisatie_cases_verificatie) AS realisatie_cases_aantal_verificatie, " & _
"Iif(IsNull(ingeplande_cases), 0, ingeplande_cases) AS ingeplande_cases_aantal, " & _
"Iif(IsNull(ingeplande_cases_verificatie), 0, ingeplande_cases_verificatie) AS ingeplande_cases_aantal_verificatie, " & _
"volgorde, "
sql = sql & "Iif(IsNull(voorraad_gisteren), 0, voorraad_gisteren) AS instroom, " & _
"Iif(IsNull(voorraad_verificatie_gisteren), 0, voorraad_verificatie_gisteren) AS instroom_verificatie "
sql = sql & "FROM tmp_planning_proces " & _
"WHERE userid = '" & EscapeString(LCase(mod_global.RealUser)) & "' " & _
"AND team_id = " & TeamID & " " & _
IIf(IsNull(MedewerkerGroepID), "AND medewerker_groep_id is null ", "AND medewerker_groep_id = " & MedewerkerGroepID & " ") & _
IIf(IsNull(Datum), "AND week = " & week & " AND jaar = " & jaar & " ", "AND datum = #" & Format(Datum, "yyyy-mm-dd") & "# ") & _
"ORDER BY volgorde ASC "
What I need to change is:
"Iif(IsNull(voorraad_gisteren), 0, voorraad_gisteren) AS instroom".
It needs to be:
"Iif(IsNull(aantal_instroom), 0, aantal_instroom) AS instroom".
The problem is that it comes from another table called instroom. The query I didn't make myself and I have limited query skills so I tried this:
"Iif(IsNull(Select aantal_instroom From instroom), 0, aantal_instroom) AS instroom"
but that doesn't work, suddenly no data appears anymore.
Does anybody know how to do this?

Answer 1

First of all there is a much better way to do:
IIf(IsNull(voorraad_gisteren), 0, voorraad_gisteren)
It is:
Nz(voorraad_gisteren, 0)
Now to your question. First you have to make sure the table instroom is part of your FROM section of the SQL statement. Example:
FROM tmp_planning_proces INNER JOIN instroom ON ... [whatever fields link the two tables together]
Then you can refer to any field on the table like this:
instroom.aantal_instroom
IIf(IsNull(instroom.aantal_instroom), 0, instroom.aantal_instroom) AS instroom
or even better:
Nz(instroom.aantal_instroom,0) AS instroom
I also agree with the comment that using the same field alias as the table name is probably a bad idea and bound to cause confusion in the future.