Altere seu ORDER BY para ordená-lo por um numérico:
ORDER BY regexp_replace(FILE_NAME, '_m', 1),
regexp_replace(FILE_NAME, '_l', 2),
regexp_replace(FILE_NAME, '_r', 3);
por exemplo.
WITH t
AS (SELECT '12345_l.tif' AS file_name FROM dual
UNION
SELECT '12345_m.tif' FROM dual
UNION
SELECT '12345_r.tif' FROM dual
UNION
SELECT '12345_x.tif' FROM dual
UNION
SELECT '12345_y.tif' FROM dual)
SELECT file_name
FROM t
ORDER BY regexp_replace(FILE_NAME, '_m', 1),
regexp_replace(FILE_NAME, '_l', 2),
regexp_replace(FILE_NAME, '_r', 3);
Dá:
==============
12345_m.tif
12345_l.tif
12345_r.tif
12345_x.tif
12345_y.tif
Espero que ajude...
Alternativamente, você pode usar:
ORDER BY (CASE SUBSTR(file_name, INSTR(file_name, '_')+1, 1)
WHEN 'm' THEN 1
WHEN 'l' THEN 2
WHEN 'r' THEN 3
ELSE 4
END) ASC;
POR EXEMPLO.:
WITH t
AS (SELECT '12345_l.tif' AS file_name FROM dual
UNION
SELECT '12345_y.tif' FROM dual
UNION
SELECT '12345_r.tif' FROM dual
UNION
SELECT '12345_x.tif' FROM dual
UNION
SELECT '12345_m.tif' FROM dual)
SELECT file_name
FROM t
ORDER BY (CASE SUBSTR(file_name, INSTR(file_name, '_')+1, 1)
WHEN 'm' THEN 1
WHEN 'l' THEN 2
WHEN 'r' THEN 3
ELSE 4
END) ASC;
Dá:
12345_m.tif
12345_l.tif
12345_r.tif
12345_x.tif
12345_y.tif
