Dejte vše do jiného SELECT:
SELECT * FROM (
SELECT "Field1" AS field_1, "Field2" AS field_2,
"Field3" AS field_3, "Field4" AS field_4
FROM "TableName"
WHERE condition
AND other_condition
UNION ALL
SELECT "Field1" AS field_1, "Field2" AS field_2,
"Field3" AS field_3, "Field4" AS field_4
FROM "TableName"
WHERE yet_another_condition
AND yet_another_other_condition
) As A
ORDER BY CASE field_1
WHEN 'A' THEN 1
WHEN 'B' THEN 2
WHEN 'C' THEN 3
ELSE 4
END
nebo, lépe, použijte alias v ORDER BY, jak je předán na konci UNION:
SELECT "Field1" AS field_1, "Field2" AS field_2,
"Field3" AS field_3, "Field4" AS field_4
FROM "TableName"
WHERE condition
AND other_condition
UNION ALL
SELECT "Field1" AS field_1, "Field2" AS field_2,
"Field3" AS field_3, "Field4" AS field_4
FROM "TableName"
WHERE yet_another_condition
AND yet_another_other_condition
ORDER BY CASE field_1
WHEN 'A' THEN 1
WHEN 'B' THEN 2
WHEN 'C' THEN 3
ELSE 4
END