CROSS APPLY

Example:

DECLARE @ABC TABLE(Letter VARCHAR(1) NOT NULL);

INSERT INTO @ABC(Letter)
VALUES('A'), ('B'), ('C');

DECLARE @123 TABLE(Number INT NOT NULL);

INSERT INTO @123(Number)
VALUES(1), (2), (3);

SELECT *
FROM @ABC
     CROSS APPLY
(
     SELECT Number
     FROM @123
) AS X;