select
sum(m.deal_qty)/count(m.deal_qty) as a,
sum(m.aveprice_amt)/count(m.aveprice_amt) as b,
t.short_str,
m.month_date
from dc_market_tproj_f m left join dc_tproject_d t on m.proj_id = t.proj_id
where m.proj_id = '5DA8C46D-FF8A-4E7B-A36B-579A1F353BC2'
and left(m.month_date,4) = convert(varchar(7),DATEADD(mm, -13, GETDATE()),120)
group by month_date,short_str
union all
select
sum(f.deal_qty)/count(f.deal_qty) as a,
sum(f.aveprice_amt)/count(f.aveprice_amt) as b,
'竞品平均' 'short_str',
f.month_date
from dc_cproject_form_d f
left join dc_cproject_d c on f.proj_id = c.proj_id
where c.tproj_id = '5DA8C46D-FF8A-4E7B-A36B-579A1F353BC2'
and left(f.month_date,4) = convert(varchar(7),DATEADD(mm, -13, GETDATE()),120)
group by month_date
union all
select
sum(f.deal_qty)/count(f.deal_qty) as a,
sum(f.aveprice_amt)/count(f.aveprice_amt) as b,
c.proj_str 'short_str',
f.month_date
from dc_cproject_form_d f
left join dc_cproject_d c on f.proj_id = c.proj_id
where c.proj_str = '${B4}'
and month_date >= convert(varchar(7),DATEADD(mm, -13, GETDATE()),120)
group by month_date,proj_str

怎么在'${B4}'有值的时候使union的第二段失效?