INSERT INTO a.grades (rollno, grade) SELECt rollno, 'A' FROM b.students WHERe ssn = 12345;
一些DBMS会接受以下内容,并在SELECt语句的周围加上括号:
INSERT INTO a.grades (rollno, grade) VALUES((SELECT rollno FROM b.students WHERe ssn = 12345), 'A');

INSERT INTO a.grades (rollno, grade) SELECt rollno, 'A' FROM b.students WHERe ssn = 12345;
一些DBMS会接受以下内容,并在SELECt语句的周围加上括号:
INSERT INTO a.grades (rollno, grade) VALUES((SELECT rollno FROM b.students WHERe ssn = 12345), 'A');