Default query for all implementations when query parameters are empty (null) in SQL Server

Method 1:
When the publisher filter condition is NULL, how do you write SQL?

1 DECLARE @publishers VARCHAR (50);
2 SELECT * FROM dbo. Book WHERE Publishers=isnull (@publishers, publishers)

Method 2:

DECLARE @cinv varchar (50)
SELECT * from inventory where 1=1 and ([email protected] or @cinv is null)

Method 3:
DECLARE @name VARCHAR (+), @page INT =1
SET @name = ' Zhang San '

DECLARE @sql VARCHAR (1000)
SET @sql = ' select * from myTable where 1=1 '
IF @name is not NULL
SET @[email protected]+ ' and name= ' [email protected]+ '--character type note the number of quotes
IF @page is not NULL
SET @[email protected]+ ' and page= ' +ltrim (@page)--int type Note convert to character type
--print @sql
EXEC (@sql)

Default query for all implementations when query parameters are empty (null) in SQL Server