CREATE TABLE enroll (stu_num VARCHAR, enroll_grade VARCHAR, class_code VARCHAR)
CREATE TABLE student (stu_lname VARCHAR, stu_num VARCHAR)

What is the last name of the student who got a grade A in the class with code 10018.
SELECT T1.stu_lname FROM student AS T1 JOIN enroll AS T2 ON T1.stu_num = T2.stu_num WHERE T2.enroll_grade = 'A' AND T2.class_code = 10018
SELECT "T1"."stu_lname" FROM "student" AS "T1" JOIN "enroll" AS "T2" ON "T1"."stu_num" = "T2"."stu_num" AND "T2"."class_code" = 10018 AND "T2"."enroll_grade" = 'A'