använd vänster koppling till tabell C
select a.*,b.*, c.DeclareDate, c.Value from TableA a
inner join TableB b on a.AI =b.BId
left join
(select * from TableC where DeclareDate='December') c
on b.BId = c.CId
OUTPUT
använd vänster koppling till tabell C
select a.*,b.*, c.DeclareDate, c.Value from TableA a
inner join TableB b on a.AI =b.BId
left join
(select * from TableC where DeclareDate='December') c
on b.BId = c.CId
OUTPUT