Show there is an implicit conversion between N'' and '' types.

ImplicitConversionUnicode.sql

USE tempdb;
GO

DROP TABLE IF EXISTS dbo.NonUnicode;
DROP TABLE IF EXISTS dbo.Unicode;
CREATE TABLE dbo.NonUnicode (NU varchar(1) NOT NULL DEFAULT 'a')
CREATE TABLE dbo.Unicode (U nvarchar(1) NOT NULL DEFAULT N'a');

INSERT INTO dbo.NonUnicode (NU) DEFAULT VALUES;
INSERT INTO dbo.Unicode (U) DEFAULT VALUES;

SELECT NU FROM dbo.NonUnicode;
SELECT U FROM dbo.Unicode;

-- Turn on 'Actual Execution Plan'.
SELECT NU, U
FROM dbo.NonUnicode
JOIN dbo.Unicode 
	ON dbo.NonUnicode.NU = dbo.Unicode.U;