DB2 SQL insert question

Dear all,
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I know that we could insert data from a table to another table by
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insert into A(F1,F2) select F1,F2 from B;
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However, it seems that DB2 doesn't have insert update for this kind of
statement (i.e. The insertion failed if primary key already exist in A,
while we could do this in import statement)
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Is that I missed something from the manuel? The work around I think of
is to delete the records beforehand, could anyone tell me whether this
could be done in the same statement?
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Thanks in advance!
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Henry
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