SQL中UNION和UNION ALL的区别
The primary difference between UNION and UNION ALL lies in how they handle duplicate rows when combining the results from two or more SELECT statements. UNION: Definition: Combines the result...
UNION和UNION ALL的区别在于重复行的处理。UNION去除重复记录，适合需要唯一结果的情况，但性能较慢。UNION ALL保留所有记录，速度更快，适合不关心重复的情况。两者要求SELECT语句的列数和数据类型一致。
