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ID  State
1      1
1      1
2      1
2      0
2      1
3      1
3      0
4      1
5      0
6      1
6      1

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select distinct id where State=1

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SQL code:
select id from idAndState
where id=1 and state =1
except
select id from idAndState
where id=1 and state<>1

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select distinct id where State=1

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select distinct id where State=1

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SQL code:
declare @t table (id varchar(50),state varchar(50))
insert into @t
select '1','1' union all
select '1','1' union all
select '2','1' union all
select '2','0' union all
select '2','1' union all
select '3','1' union a