Lookup (or) Drop-down for field in Dynamic AX using query

void lookupField(FormControl  control)
{
    Query                   query = new Query();
    QueryBuildDataSource    queryBuildDataSource;
    QueryBuildRange         queryBuildRange;
    SysTableLookup          sysTableLookup;
    ;

    //Create an instance of SysTableLookup with the form control passed in
    sysTableLookup = SysTableLookup::newParameters(tablenum(<table name>), control);

    //Add the fields to be shown in the lookup form
    sysTableLookup.addLookupfield(fieldnum(<table name>, <field name>), true);
    sysTableLookup.addLookupfield(fieldnum(<table name>, <field name>), false);

    //create the query datasource
    queryBuildDataSource = query.addDataSource(tablenum(<table name>));
    queryBuildRange = queryBuildDataSource.addRange(fieldnum(<table name>, <field name>));
    queryBuildRange.value(enum2str(NoYes::Yes)); //Example of Enum value or you can specify any range

    //add the query to the lookup form
    sysTableLookup.parmQuery(query);

    // Perform lookup
    sysTableLookup.performFormLookup();
}

Lookup using temporary table:

Writing the lookup under form > datasource > field  > method:

public void lookup(FormControl _formControl, str _filterStr)

{

    Query                       query          = new Query();

    QueryBuildDataSource        qds1;

    QueryBuildDataSource        qds2;

    QueryBuildRange             qr1;

    QueryBuildRange             qr2;

    QueryBuildRange             qr3;

    SysTableLookup              sysTableLookup;

    VendInvoiceJour             VendInvoiceJour;

    WHT_WithholdingTaxTrans     WHT_WithholdingTaxTrans;

    WHT_KRALookuptable          WHT_KRALookuptable; // Temporary table

    QueryRun                    qr;

    ;

    delete_from WHT_KRALookuptable;

    qds1 = query.addDataSource(tableNum(VendInvoiceJour));

    qds2 = qds1.addDataSource(tableNum(WHT_WithholdingTaxTrans));

    qds2.joinMode(JoinMode::InnerJoin);

    qds2.addLink(fieldNum(WHT_WithholdingTaxTrans,Invoice), fieldNum(VendInvoiceJour,InvoiceId));

    qds2.addLink(fieldNum(WHT_WithholdingTaxTrans,InvoiceAccount), fieldNum(VendInvoiceJour,InvoiceAccount));

    qr1 = qds1.addRange(fieldNum(VendInvoiceJour, InvoiceAccount));

    qr1.value(WHT_KRAreceiptUpdate.AccountNum);

    qr2 = qds2.addRange(fieldNum(WHT_WithholdingTaxTrans, WHT_KRAStatus));

    qr2.value(int2str(WHT_KRAStatus::Paid));

    qr3 = qds2.addRange(fieldNum(WHT_WithholdingTaxTrans,WHT_DTA));

    qr3.value(int2str(NoYes::No));

    qr = new QueryRun(query);

    while (qr.next())

    {

        VendInvoiceJour = qr.get(tablenum(VendInvoiceJour));

        select WHT_KRALookuptable

            where WHT_KRALookuptable.InvoiceId == VendInvoiceJour.InvoiceId

            && WHT_KRALookuptable.InvoiceAmount == VendInvoiceJour.InvoiceAmount;

        if (!WHT_KRALookuptable)

        {

            select sum(WithholdingTaxAmount) from  WHT_WithholdingTaxTrans

                group by InvoiceAccount,Invoice

                where WHT_WithholdingTaxTrans.InvoiceAccount == VendInvoiceJour.InvoiceAccount

                && WHT_WithholdingTaxTrans.Invoice == VendInvoiceJour.InvoiceId;

            if (WHT_WithholdingTaxTrans)

            {

                WHT_KRALookuptable.WithholdingTaxAmount = WHT_WithholdingTaxTrans.WithholdingTaxAmount;

            }

            WHT_KRALookuptable.InvoiceId = VendInvoiceJour.InvoiceId;

            WHT_KRALookuptable.InvoiceAmount = VendInvoiceJour.InvoiceAmount;

            WHT_KRALookuptable.AccountNum = VendInvoiceJour.InvoiceAccount;

            WHT_KRALookuptable.insert();

        }

    }

    sysTableLookup = SysTableLookup::newParameters(tableNum(WHT_KRALookuptable),_formControl);

    sysTableLookup.addLookupField(fieldNum(WHT_KRALookuptable, InvoiceId));

    sysTableLookup.addLookupField(fieldNum(WHT_KRALookuptable, InvoiceAmount));

    sysTableLookup.addLookupField(fieldNum(WHT_KRALookuptable, WithholdingTaxAmount));

    //sysTableLookup.parmQuery(query);

    sysTableLookup.performFormLookup();

}