Using the EXISTS Operator with subquery : EXISTS « Query Select « Oracle PL/SQL Tutorial

1. Oracle PL/SQL Tutorial
2. Query Select
3. EXISTS

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.