# 1797 Executing Multiple INSERT, UPDATE, or DELETE Queries Can Cause a Memory Leak

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I've been tracking down a memory leak and found that if you use a prepared query that updates, deletes or inserts with a sub-select more than once you will leak a TStringList assigned to FTransactionTables in TDataQuery, ie something like:

UpdateQuery.SQL.Clear;
UpdateQuery.SQL.Add.. {Update delete or insert with sub-select SQL}
UpdateQuery.Prepare;
UpdateQuery.ExecSQL;
UpdateQuery.ExecSQL; /// Leaks here

This affects a lot of our code where we update items at regular intervals. The reason is that in dbisamsq at lines 7948, 8116 & 8321 (ExecuteSubSelectInsertQuery, ExecuteUpdateQuery & ExecuteDeleteQuery respectively) a new TStringList is created and assigned to FTransactionTables and for a prepared query when executing repeatedly this variable is already assigned.