Mysql使用Union结果不满足预期的问题_union注入回显显示不全-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_36323559/article/details/98492165

在处理业务需求时，遇到一个使用UNION的MySQL查询，发现查询结果只包含了第二个SELECT语句的数据。经过排查，发现在UNION关键字后添加小括号可以解决问题，使得预期的UNION结果得以正确显示。

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今天业务需求中需要用到UNION，SQL如下：

select p.id as id, p.`column` as `column`, p.`value` as `value`, p.history_begin_time as history_begin_time, p.history_end_time as history_end_time 
from cmdbcoresvrdb.p_fixednetworkelement p 
WHERE p.id = 0x11E8A2BD695CD4C692DB286ED288C859 and p.history_begin_time >= 1564649660400 and p.history_end_time <= 1564649840600 
UNION 
select p.id as id, p.`column` as `column`, p.`value` as `value`, p.history_begin_time as history_begin_time, p.history_end_time as history_end_time 
from cmdbcoresvrdb.p_fixednetworkelement p 
WHERE p.id = 0x11E8A2BD695CD4C692DB286ED288C859 and p.history_begin_time < 1564649660400
ORDER BY history_begin_time DESC LIMIT 1

运行之后发现UNION执行不正常，只有后边select的结果
后来在UNION后边加上了小括号，问题解决

select p.id as id, p.`column` as `column`, p.`value` as `value`, p.history_begin_time as history_begin_time, p.history_end_time as history_end_time 
from cmdbcoresvrdb.p_fixednetworkelement p 
WHERE p.id = 0x11E8A2BD695CD4C692DB286ED288C859 and p.history_begin_time >= 1564649660400 and p.history_end_time <= 1564649840600 
UNION 
(select p.id as id, p.`column` as `column`, p.`value` as `value`, p.history_begin_time as history_begin_time, p.history_end_time as history_end_time 
from cmdbcoresvrdb.p_fixednetworkelement p 
WHERE p.id = 0x11E8A2BD695CD4C692DB286ED288C859 and p.history_begin_time < 1564649660400
ORDER BY history_begin_time DESC LIMIT 1)