MySQL UNION截断返回的数据集

Question

SELECT current_raised,segment FROM gizmos
where created_at >= "2012-03-01"

返回600多行

SELECT "current_raised","segment"
UNION
(SELECT current_raised,segment FROM gizmos
where created_at >= "2012-03-01")

返回180行

为什么会这样？

Answer 1

union将从结果集中删除每个重复的current_raised, segment对.试试吧union all.

以下是正在发生的事情的缩减示例.