Adding and filling new column on big table

I have a table of about 500,000 rows.

I need to add a new column and populate it.

So, I have tried to run the following command. The command never finishes (I
gave up after about and hour and a half!).

Note that none of the columns have indexes.

Update mytable set new_column =

case when column_1 = column_2
then 1

when column_1+column_3= column_2 and column_3 > 0
then 2

when column_1+column_3+column_4 = column_2 and column_4 > 0
then 3

when column_1+column_3+column_4+column_5 = column_2 and column_5 > 0
then 4

else
0

end

My computer is a Pentium 4 – 2.4 GHZ and 1G RAM – so it should be fast
enough.

Any ideas?

Jonathan Blitz

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