SELECT `id` FROM `table` WHERE 1000 IN (`field1`, `field2`, `field2`)
SELECT `id` FROM `table` WHERE `field1` IN (1000, 2000, 3000)
SELECT `id`, `fieldN` FROM `table` WHERE (1000, 2000, 3000) IN (`field1`, `field2`, `field2`)
id | fieldN
33 | 1000
56 | 2000
65 | 3000