SQL left join, used to display associated content on the website

Select Blogarticle. * , Blogarticleclass. Title As Classtitle From Blogarticle Left   Join Blogarticleclass On Blogarticleclass. ID = Blogarticle. classid

 

The role of the following section is:

Displays the first five excellent content in BBS.
And displays the number of posts (postcount) for the title (BBS. Title) nickname (userinfo. Nickname) Avatar (userinfo. Face)

Select   Top   5 BBS. * , Userinfo. Nickname As Nickname, userinfo. Face As Face,
Isnull ( Temp . Count , 0 ) As Postcount
From BBS Left   Join
Userinfo On Userinfo. Username = BBS. Username Left   Join
( Select Belong, Count ( * ) As   Count
From BBS
Group   By Belong) As   Temp   On   Temp . Belong = BBS. ID
Where BBS. isgreat =   1   And BBS. Belong =   0