选择一列为“val”的条目，然后选择“aaa”，然后选择“ccc”

How to order entries by one column (let's say named column13). First should be entries where column13 is "val", then "aaa", then "ccc". I can't use GROUP BY column13 ASC or similar. Is it possible to do it without writing 3 queries?

Use the FIELD() construct available in MySQL:

SELECT       stuff
    FROM     table
    WHERE    condition
    ORDER BY FIELD(column13, 'val', 'aaa', 'ccc')