# 2458 Parameterized UNION Queries Causing Access Violation

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I get "invalid pointer operation" errormessages on some TEDBQuery components when I call the Close method. I have two Tables: Project and ProjectStructure (see below). I will combine these two tables with the following SQL command.

When I run this command, then all seems ok, I get correct result. Now I call the command the second time, I check the TEDBQuery component.Active property and close:

if qryObjectsList.Active then
qryObjectsList.Close; // sometimes I get here the invalid pointer op

qryObjectsList.SQL.Clear; // here when I try to access the SQL property I
// get an AV
qryObjectsList.SQL.Add(SQLCommand see above);
qryObjectsList.Prepare;
qryObjectsList.Open;
....

When I'm changing my SQL command to select only the first or second part (without union) all seem working fine.