select (select count(*) as temp from table1
where conditions)+
(select count(*) as temp from table2
where conditions)+
(select count(*) as temp from table3
where conditions)
where conditions)+
(select count(*) as temp from table2
where conditions)+
(select count(*) as temp from table3
where conditions)
(
select count(*) as temp from table1
where conditions
union all
select count(*) as temp from table2
where conditions
union all
select count(*) as temp from table3
where conditions
...
)AAA
select count(*) as temp from table1
where conditions
union all
select count(*) as temp from table2
where conditions
union all
select count(*) as temp from table3
where conditions
) aa
where conditions)+
(select count(*) from table2
where conditions)+
(select count(*) from table3
where conditions) as temp