Joining master and child with only the row count of child table - sql-server

Question

Master Table:
CREATE TABLE [dbo].[db_Chat](
[ChatID] [int] IDENTITY(1,1) NOT NULL,
[MemberID] [int] NOT NULL,
[MsgText] [nvarchar](300) COLLATE Chinese_Taiwan_Stroke_CI_AS NOT NULL,
[DateCreated] [smalldatetime] NOT NULL,
CONSTRAINT [PK_db_Chat] PRIMARY KEY CLUSTERED
(
[ChatID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
Child Table:
CREATE TABLE [dbo].[db_Chat_Read](
[ChatReadID] [int] IDENTITY(1,1) NOT NULL,
[MemberID] [int] NOT NULL,
[ChatID] [int] NOT NULL,
[DateCreated] [smalldatetime] NOT NULL,
CONSTRAINT [PK_db_Chat_Read] PRIMARY KEY CLUSTERED
(
[ChatReadID] ASC
)WITH (IGNORE_DUP_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
I want to join the two tables and show the number of rows of child table, if there is no row selected then it can show zero.
I know the following code works fine.
select c.ChatID, COUNT(*) as ACount from db_chat c
left join db_Chat_Read r
on c.ChatID = r.ChatID
where c.ChatGroupID=2
GROUP BY c.ChatID
But I need something like this in a single SQL code, the following SQL code is invalid, but it is to show what result I want: I need full fields of master table with only Row Count of child table.
select c.*, COUNT(r.*) from db_chat c
left join db_Chat_Read r
on c.ChatID = r.ChatID
where c.ChatGroupID=2
Thank you~!

Answer 1

You can do what you want with a subquery:
select c.*,
(select COUNT(*) from db_Chat_Read r where c.ChatID = r.ChatId
) as ACount
from db_chat c
where c.ChatGroupID = 2;
However, I would recommend putting the columns in the group by.
EDIT:
You can also do this with an additional join:
select c.*, coalesce(ACount, 0) as ACount
from db_chat c left join
(select r.ChatId, count(*) as ACount
from db_Chat_Read r
group by r.ChatId
) r
on c.ChatID = r.ChatID
where c.ChatGroupID = 2;