0 - 1 of 1 tags for all-amps sum step

Hi,

I have a salary_table and I want to fetch the maximum of Net_Amt from that.
I want to know how does teradata get this maximum value.So I get the explain plan which is as follows:

explain
sel max(Net_Amt) from dbname.salary_table;
Explanation
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1) First, we lock a distinct dbname."pseudo table" for read on a
RowHash to prevent global deadlock for dbname.salary_table.
2) Next, we lock dbname.salary_table for read.
3) We do an all-AMPs SUM step to aggregate from