create table x(col varchar(10))
insert into x values('true') 
insert into x values('true') 
insert into x values('true') 
insert into x values('true') 
insert into x values('false') 
insert into x values('false') 
go

select col , count(*) cnt from x group by col

--drop table col

/*
col        cnt         
---------- ----------- 
false      2
true       4

（所影响的行数为 2 行）
*/

------解决方案--------------------
只有两种的话，不用group也行：
SQL code
select col='true', cnt=count(1) from tb where col='true'
union all
select col='false', cnt=count(1) from tb where col='false'

------解决方案--------------------

select col, [count] = case col when 'true' then count(col) else count(col) end  
from X
group by col

------解决方案--------------------
SQL code
select col,count(1) from x group by col