Mega Code Archive

Using the EXISTS Operator with subquery

SQL> CREATE TABLE empExam ( 2 empID INT NOT NULL, 3 ExamID INT NOT NULL, 4 Mark INT, 5 Taken SMALLINT, 6 Comments VARCHAR(255), 7 CONSTRAINT PK_empExam PRIMARY KEY (empID, ExamID)); Table created. SQL> SQL> SQL> INSERT INTO empExam (empID,ExamID,Mark,Taken,Comments) VALUES (1,1,55,1,'Satisfactory'); 1 row created. SQL> INSERT INTO empExam (empID,ExamID,Mark,Taken,Comments) VALUES (1,2,73,1,'Good result'); 1 row created. SQL> INSERT INTO empExam (empID,ExamID,Mark,Taken,Comments) VALUES (2,3,44,1,'Hard'); 1 row created. SQL> INSERT INTO empExam (empID,ExamID,Mark,Taken,Comments) VALUES (2,5,39,0,'Simple'); 1 row created. SQL> INSERT INTO empExam (empID,ExamID,Mark,Taken) VALUES (2,6,63,1); 1 row created. SQL> SQL> SQL> SQL> CREATE TABLE emp ( 2 empID INT NOT NULL PRIMARY KEY, 3 Name VARCHAR(50) NOT NULL); Table created. SQL> INSERT INTO emp (empID,Name) VALUES (1,'Tom'); 1 row created. SQL> INSERT INTO emp (empID,Name) VALUES (2,'Jack'); 1 row created. SQL> INSERT INTO emp (empID,Name) VALUES (3,'Mary'); 1 row created. SQL> INSERT INTO emp (empID,Name) VALUES (4,'Bill'); 1 row created. SQL> INSERT INTO emp (empID,Name) VALUES (5,'Cat'); 1 row created. SQL> INSERT INTO emp (empID,Name) VALUES (6,'Victor'); 1 row created. SQL> SQL> SQL> SELECT empID, Name FROM emp s 2 WHERE EXISTS ( 3 SELECT empID FROM empExam e 4 WHERE Mark < 40 AND e.empID = s.empID); EMPID NAME ---------- -------------------------------------------------- 2 Jack 1 row selected. SQL> SQL> SQL> SQL> drop table emp; Table dropped. SQL> drop table empExam; Table dropped.