例如，我有表table，有两个字段id, field1,其中id为自增长字段，field1为nvarchar(50),表结构如下：
id field1
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1 a
2 b
3 a
4 c
5 a
6 b

我想用一SQL语句，实现从数据库中提取出id及field1的数值，其中field1中的a,b,c只提取一次。
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distinct
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select max(id),field1 from tabel group by field1

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select min(a.id),b.field1
from table1 a,(select distinct field1 from table1) b
where a.field1=b.field1
group by a.id
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select min(id),field1 from tabel group by field1也行
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select *
from T a
where id in (select max(id)
from T
where field1 = a.field1)

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select min(id), field1 from T group field1