本文讨论了如何通过在SQL查询中使用withtas和分发排序算法（如distributebyrand()和sortbyrand())，结合UNIONALL操作，来提升从表中随机获取数据的效率，特别指出orderbyrand()效率较低，而上述方法更优。
with t as (
select 1 id
union all select 2
union all select 3
union all select 4
union all select 5
union all select 6
union all select 7
union all select 8
union all select 9
union all select 10
)
select
*
,id % 2 as id2
from t
distribute by rand()
sort by rand()
LIMIT 5
-- order by rand() 随机效率较低，上述效率较高
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