Finding positive and negative values that match

Question

I would need to find values that are the same, but positive and negative.
The table could look like :
ID INV_AMOUNT
1 100
2 200
3 -100
I would need to write a select statement that would only find
ID INV_AMOUNT
1 100
3 -100
Any help would be much appreciated

Answer 1

you take two numbers then if the absolut value from the two numbers are equal you can select them
now you try each combination and select all matches
I hope you understand what I mean my English is not so good