您可以
union在不同时间进行几个查询：
(SELECt id, a_time AS time, metadata1, metadata2 FROM mytable)UNIOn(SELECt id, b_time AS time, metadata1, metadata2 FROM mytable)UNIOn(SELECt id, c_time AS time, metadata1, metadata2 FROM mytable)UNIOn(SELECt id, d_time AS time, metadata1, metadata2 FROM mytable)ORDER BY time
