Dynamic SQL statement execution usage

1. Use the exec (@ sq lstr) method. @ sqlstr is a string to be executed and dynamically connects various conditions through this string.
2. run the sp_executesql stored procedure. The Code is as follows:
declare @ tablename varchar (50)
declare @ A varchar (50)
declare @ B varchar (50)
declare @ SQL nchar (500) -- Note that varchar cannot be used

set @ A = 'A'
set @ B = 'B'
set @ tablename = 'dbo. table_1 '
set @ SQL = n' insert into' + @ tablename + 'values (@ A, @ B) '
exec sp_executesql @ SQL, n' @ A varchar (50), @ B varchar (50) ', @ A, @ B