Stored procedure to create or update - sql-server

Question

I am working on creating a Web API which will get account as the input parameter, which will have to create / update records in the table in SQL Server. So the web service will need to call the stored procedure which will accept the account. I created a sample table in the database with just two columns called Account and CounterSeq. I am trying to creating a stored procedure to create or update the records in the table.
Each account should have a CounterSeq associated with it. If the Account doesn't exists in the table, create Account name and associate CounterSeq = 001 to it. If the Account name already exists, just update like CounterSeq to CounterSeq + 1
+---------+----------------+
| Account | CounterSeq |
+---------+----------------+
| ABC | 001 |
| DEF | 002 |
+---------+----------------+
For this I create a TableType like this
USE [Demo]
GO
-- Create the data type
CREATE TYPE projectName_TT AS TABLE
(
Account nvarchar(50),
CounterSeq int
)
GO
And the stored procedure as below but I am missing how to insert the new record like for a new Account how to set the CounterSeq to 001 ?
USE [Demo]
GO
ALTER PROCEDURE [dbo].[uspInserorUpdateProjectName]
#projectName_TT AS projectName_TT READONLY
AS
BEGIN
SET NOCOUNT ON;
BEGIN TRANSACTION;
UPDATE prj
SET prj.Account = tt.Account,
prj.CounterSeq = tt.CounterSeq + 1
FROM dbo.[ProjectName] prj
INNER JOIN #projectName_TT tt ON prj.Account = tt.Account
INSERT INTO [dbo].[ProjectName](Account, CounterSeq)
SELECT tt.Account, tt.CounterSeq
FROM #projectName_TT tt
WHERE NOT EXISTS (SELECT 1
FROM [dbo].[ProjectName]
WHERE Account = tt.Account)
COMMIT TRANSACTION;
END;

Answer 1

First, I believe that the table you passed in should only have one field (based on your description If the Account doesn't exists in the Database create Account name and associate CounterSeq 001 to it. If the Account name already exists just update like CounterSeq to CounterSeq+1)
You can use this query (put it in your stored procedure between the BEGIN TRANSACTION, COMMIT TRANSACTION.
MERGE dbo.[ProjectName] prj
USING #projectName_TT tt
ON prj.Account = tt.Account
WHEN MATCHED THEN UPDATE SET prj.CounterSeq = prj.CounterSeq+1
WHEN NOT MATCHED THEN INSERT (Account,CounterSeq)
VALUES (tt.Account, 1);