union
-- union 会对所有重复对内容去重
select
category
from
(
select
1 as category
union all
select
1 as category
)tmp
union
select
1 as category -- union 会对所有重复对内容去重
select
category
from
(
select
1 as category
union all
select
1 as category
)tmp
union
select
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