说我有下表：
================================================= | color_id | parent_id | language_id | name | ================================================= | 1 | 50 | 1 | Black | -------------------------------------------------
然后说我需要排WHERE parent_id = 50 AND language_id = 2。显然，基于示例表，我什么也得不到。但是，我仍然需要一个结果-大概是这样的：
WHERE parent_id = 50 AND language_id = 2
================================================= | color_id | parent_id | language_id | name | ================================================= | NULL | 50 | 2 | NULL | -------------------------------------------------
有没有办法在SQL中做到这一点？
您可以对可能有效的记录和默认记录进行联合查询，然后选择第一个：
SELECT * FROM (SELECT color_id, parent_id, language_id, name, 1 as order_rank FROM some_table WHERE parent_id = %parent_id% AND language_id = %language_id% UNION SELECT NULL, %parent_id%, %language_id%, NULL, 2 as order_rank ) ORDER BY order_rank LIMIT 1
（根据OMG Ponies的建议，使用静态值进行编辑以进行订购）
