id    name
1      a
2      b
3      c

id    id_t1   f1
1       1     a1
2       1     a2
3       3     c1

id    name
1      a
3      c

select * from #t1 a where not exists(select 1 from #t2 where id_t1=a.id)

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探讨


SQL code
select * from #t1 a where not exists(select 1 from #t2 where id_t1=a.id)


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探讨

SQL code

select * from #t1 a where not exists(select 1 from #t2 where id_t1=a.id)


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探讨

引用:
SQL code

select * from #t1 a where not exists(select 1 from #t2 where id_t1=a.id)


把not去掉就可以了。
--或者：用嵌套子查询

SQL code

select * from t1 where id in(select id_t1 from t2)


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探讨

根据字段#t2.id_t1与#t1.id关联，如果从表#t2没数据没有对应主表，则显示主表的数据来