我在PostgreSQL中有此数据
Id type quantity
1 order 10
2 order 12
3 order 11
4 purchase 5
5 purchase 4
6 credit 2
当type=‘Order’或‘Credit’时,我想退货数量为负数
Id type quantity
1 order -10
2 order -12
3 order -11
4 purchase 5
5 purchase 4
6 credit -2
我如何在PostgreSQL中做到这一点?