Your call to fetchall_arrayref returns ALL ROWS.

So, your first dereference gets you an array of Rows (Your array has only one element).

Now, you need to dereference again to get to the value stored within column(0) of that row.

You can accomplish all this in a single step:

 
 my $wb_runkey = $aryRef->[0]->[0];
 # Can also be written as :
 #     $aryRef->[0][0];  # Arrow in between is implied
 #     ${$aryRef}[0][0]; # Look ma - no arrows (But this is uglier, IM
+HO)
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Hopefully, this exercise dipped your toe into dereferencing - an extremely powerful construct, for advancing with perl.