Você pode usar um
UNION , que removerá as duplicatas (enquanto UNION ALL manterá as duplicatas) SELECT FirstUrlColumn AS url
FROM myTable
UNION
SELECT secondUrlColumn AS url
FROM myTable
UNION , que removerá as duplicatas (enquanto UNION ALL manterá as duplicatas) SELECT FirstUrlColumn AS url
FROM myTable
UNION
SELECT secondUrlColumn AS url
FROM myTable