problem with SUM,COUNT etc. results in SQL

[Moron]

Sorry if this is too stupid question (and sorry for my english too) I tried to find some solution but wasn't successful.

I am not able to obtain results of SQL functions like SUM,MAX, LAST_INSERT_ID() with IZStatement like You can see below

Part of my code:

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var
      	sqlDotaz : string;
        statement : IZStatement;
        resultSet : IZResultSet;
      begin
        statement := dmCentral.dmCentralni.zCentrKonekt.DbcConnection.CreateStatement;
        sqlDotaz := 'select Sum(pocet_volnych) from typ_materialu';
        resultSet := Statement.ExecuteQuery(sqlDotaz);
        sumVolnych := resultSet.GetLong(1);

when program executes

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 resultSet.GetLong(1);

it colaps and write error "row data is not available"
TZMySQLResultSet.FRowHandle=nil but I really don't know why. Can someone please please help?

[Moron]

After many hours I finally figure it out. So For everyone who has a similar problem:

Ensure that You call at least once

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 resultSet.next

before you try to call something like

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resultSet.GetLong(1)