SQL Merge Syntax Single table query

--The project needs to use the Merg grammar, so went online to check the data, found that it is a multi-table query, the problem is that I only have a table, so I am puzzled, and then I brainwave, it's done!
--Table name: T_login (Login table)
--field: F_username (username), f_status (login status 0 = logged in)
--Execution requirements: When the user logs on, if the user is present, the modification status is 0, and if it does not exist, add a record
--Define the parameters:
DECLARE @f_userName varchar (20)
Set @f_userName = ' Test '
DECLARE @f_status int
Set @f_status =0
--Syntax format
Merge into T_login as A
--Joint query, at the same time the T_login table as a condition table, need to use the fields are detected, here directly to the field query out use, in fact, single table and multi-table is a meaning, passed in only parameters, not related to the table
Using (select @f_userName f_username) as b--here if there are multiple conditions, you can also use commas to separate them, such as select @f_userName F_username, @f_status f_status
--Judging conditions
On (a.f_username=b.f_username)--if there are more conditions, you can use and add to the following, such as A.f_status=b.f_status
-If there is
When matched then
--Update status
Update Set F_status=0
--If not present
When isn't matched then
--Insert new data
Insert (F_username,f_status)
--The last semicolon must be added, which is the syntax format
Values (b.f_username,0);

SQL Merge Syntax Single table query