Problems with SQL like statements in Microsoft enterpriselibrary

The following is a piece of code when Microsoft javasiselibrary is used:

Public datatable getcontractreportdata (string username)
{
Database DB = databasefactory. createdatabase ("sqldbconnection ");
String SQL = @ "select
[Username]
, [Birthday]
From [userinfo]
Where 1 = 1 and [username] Like '% @ username % '";
Datatable dt = new datatable ();
Using (dbcommand cmd = dB. getsqlstringcommand (SQL ))
{
DB. addinparameter (CMD, "@ username", dbtype. String, username );
Dt = dB. executedataset (CMD). Tables [0];
}

Return DT;
}
After the above code is executed, an empty record is returned, which indicates that there is data in the database. After careful research, it is found that there is a problem with the use of the like statement, as long as the Code marked in red in the above example is replaced
Where 1 = 1 and [username] Like '%' + @ username + '% '";
After the program is executed, records can be normally returned.