Oracle PL/SQL/Subquery/Correlated Subquery

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A correlated subquery references one or more columns in the outer query

  

SQL> CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
  2                    ENAME VARCHAR2(10),
  3                    JOB VARCHAR2(9),
  4                    MGR NUMBER(4),
  5                    HIREDATE DATE,
  6                    SAL NUMBER(7, 2),
  7                    COMM NUMBER(7, 2),
  8                    DEPTNO NUMBER(2));
Table created.
SQL>
SQL> INSERT INTO EMP VALUES (7369, "SMITH", "CLERK",    7902, TO_DATE("17-DEC-1980", "DD-MON-YYYY"), 800, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7499, "ALLEN", "SALESMAN", 7698, TO_DATE("20-FEB-1981", "DD-MON-YYYY"), 1600, 300, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7521, "WARD",  "SALESMAN", 7698, TO_DATE("22-FEB-1981", "DD-MON-YYYY"), 1250, 500, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7566, "JONES", "MANAGER",  7839, TO_DATE("2-APR-1981",  "DD-MON-YYYY"), 2975, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7654, "MARTIN", "SALESMAN", 7698,TO_DATE("28-SEP-1981", "DD-MON-YYYY"), 1250, 1400, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7698, "BLAKE", "MANAGER", 7839,TO_DATE("1-MAY-1981", "DD-MON-YYYY"), 2850, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7782, "CLARK", "MANAGER", 7839,TO_DATE("9-JUN-1981", "DD-MON-YYYY"), 2450, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES (7788, "SCOTT", "ANALYST", 7566,TO_DATE("09-DEC-1982", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7839, "KING", "PRESIDENT", NULL,TO_DATE("17-NOV-1981", "DD-MON-YYYY"), 5000, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES (7844, "TURNER", "SALESMAN", 7698,TO_DATE("8-SEP-1981", "DD-MON-YYYY"), 1500, 0, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7876, "ADAMS", "CLERK", 7788,TO_DATE("12-JAN-1983", "DD-MON-YYYY"), 1100, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7900, "JAMES", "CLERK", 7698,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 950, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7902, "FORD", "ANALYST", 7566,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7934, "MILLER", "CLERK", 7782,TO_DATE("23-JAN-1982", "DD-MON-YYYY"), 1300, NULL, 10);
1 row created.
SQL>
SQL> select * from emp;
     EMPNO ENAME      JOB              MGR HIREDATE           SAL       COMM     DEPTNO
---------- ---------- --------- ---------- ----------- ---------- ---------- ----------
      7369 SMITH      CLERK           7902 1980-DEC-17        800                    20
      7499 ALLEN      SALESMAN        7698 1981-FEB-20       1600        300         30
      7521 WARD       SALESMAN        7698 1981-FEB-22       1250        500         30
      7566 JONES      MANAGER         7839 1981-APR-02       2975                    20
      7654 MARTIN     SALESMAN        7698 1981-SEP-28       1250       1400         30
      7698 BLAKE      MANAGER         7839 1981-MAY-01       2850                    30
      7782 CLARK      MANAGER         7839 1981-JUN-09       2450                    10
      7788 SCOTT      ANALYST         7566 1982-DEC-09       3000                    20
      7839 KING       PRESIDENT            1981-NOV-17       5000                    10
      7844 TURNER     SALESMAN        7698 1981-SEP-08       1500          0         30
      7876 ADAMS      CLERK           7788 1983-JAN-12       1100                    20
      7900 JAMES      CLERK           7698 1981-DEC-03        950                    30
      7902 FORD       ANALYST         7566 1981-DEC-03       3000                    20
      7934 MILLER     CLERK           7782 1982-JAN-23       1300                    10
14 rows selected.
SQL>
SQL> --Writing Correlated Subqueries
SQL>
SQL> --A correlated subquery references one or more columns in the outer query.
SQL> --The subquery is known as a correlated subquery because the subquery is related to the outer query.
SQL>
SQL> SELECT empno, mgr,ename, sal
  2  FROM emp outer
  3  WHERE sal >
  4    (SELECT AVG(sal)
  5     FROM emp inner
  6     WHERE inner.empno = outer.mgr);
     EMPNO        MGR ENAME             SAL
---------- ---------- ---------- ----------
      7788       7566 SCOTT            3000
      7902       7566 FORD             3000
SQL>
SQL>
SQL> drop table emp;
Table dropped.
SQL>
SQL>



A correlated subquery: the subquery references a column from a table referred to in the parent statement.

  
SQL>
SQL> CREATE TABLE EMP(
  2      EMPNO NUMBER(4) NOT NULL,
  3      ENAME VARCHAR2(10),
  4      JOB VARCHAR2(9),
  5      MGR NUMBER(4),
  6      HIREDATE DATE,
  7      SAL NUMBER(7, 2),
  8      COMM NUMBER(7, 2),
  9      DEPTNO NUMBER(2)
 10  );
Table created.

SQL> INSERT INTO EMP VALUES(2, "Jack", "Tester", 6,TO_DATE("20-FEB-1981", "DD-MON-YYYY"), 1600, 300, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(3, "Wil", "Tester", 6,TO_DATE("22-FEB-1981", "DD-MON-YYYY"), 1250, 500, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(4, "Jane", "Designer", 9,TO_DATE("2-APR-1981", "DD-MON-YYYY"), 2975, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES(5, "Mary", "Tester", 6,TO_DATE("28-SEP-1981", "DD-MON-YYYY"), 1250, 1400, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(6, "Black", "Designer", 9,TO_DATE("1-MAY-1981", "DD-MON-YYYY"), 2850, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(7, "Chris", "Designer", 9,TO_DATE("9-JUN-1981", "DD-MON-YYYY"), 2450, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES(8, "Smart", "Helper", 4,TO_DATE("09-DEC-1982", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES(9, "Peter", "Manager", NULL,TO_DATE("17-NOV-1981", "DD-MON-YYYY"), 5000, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES(10, "Take", "Tester", 6,TO_DATE("8-SEP-1981", "DD-MON-YYYY"), 1500, 0, 30);
1 row created.

SQL> INSERT INTO EMP VALUES(13, "Fake", "Helper", 4,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.

SQL>
SQL> CREATE TABLE DEPT(
  2      DEPTNO NUMBER(2),
  3      DNAME VARCHAR2(14),
  4      LOC VARCHAR2(13)
  5  );
Table created.
SQL>
SQL> INSERT INTO DEPT VALUES (10, "ACCOUNTING", "NEW YORK");
1 row created.
SQL> INSERT INTO DEPT VALUES (20, "RESEARCH", "DALLAS");
1 row created.
SQL> INSERT INTO DEPT VALUES (30, "SALES", "CHICAGO");
1 row created.
SQL> INSERT INTO DEPT VALUES (40, "OPERATIONS", "BOSTON");
1 row created.
SQL>
SQL>
SQL> SELECT deptno, ename, sal
  2      FROM   emp e1
  3      WHERE  sal = (SELECT MAX(sal) FROM emp
  4                       WHERE  deptno = e1.deptno)
  5
SQL> drop table emp;
Table dropped.
SQL> drop table dept;
Table dropped.
SQL>



Get Categories and Products (with Correlated Subqueries)

  
SQL> CREATE TABLE Product (
  2  ProductID INT NOT NULL PRIMARY KEY,
  3  Name VARCHAR(50) NOT NULL,
  4  Description VARCHAR(1000) NOT NULL,
  5  Price NUMBER NULL,
  6  ImagePath VARCHAR(50) NULL,
  7  soldout NUMBER(1,0) NULL,
  8  Promotion NUMBER(1,0) NULL);
Table created.
SQL>
SQL> CREATE SEQUENCE ProductIDSeq;
Sequence created.
SQL>
SQL> CREATE OR REPLACE TRIGGER ProductAutonumberTrigger
  2  BEFORE INSERT ON Product
  3  FOR EACH ROW
  4  BEGIN
  5     SELECT ProductIDSeq.NEXTVAL
  6     INTO :NEW.ProductID FROM DUAL;
  7  END;
  8  /
Trigger created.
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath,soldout, Promotion)
  2  VALUES ("Pen", "Ball Pen",5.99, "pen.jpg", 1, 0);
1 row created.
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("Ruler", "Long",14.99, "ruler.jpg", 0, 0);
1 row created.
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("Desk", "Computer Desk",5.99, "desk.jpg", 0, 1);
1 row created.
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("PC", "Notebook",49.99, "pc.jpg", 0, 1);
1 row created.
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("Mouse", "Wireless",9.99, "mouse.jpg",  1, 0);
1 row created.
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("Keyboard", "keyboard",3.75, "keyboard.jpg", 0, 0);
1 row created.
SQL>
SQL>
SQL>
SQL> CREATE TABLE ProductCategory (
  2  ProductID INT NOT NULL,
  3  CategoryID INT NOT NULL,
  4  PRIMARY KEY (ProductID, CategoryID)
  5  );
Table created.
SQL>
SQL>
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (1,3);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (2,1);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (2,3);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (3,3);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (4,1);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (5,2);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (6,3);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (6,4);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (7,4);
1 row created.
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (8,5);
1 row created.
SQL>
SQL>
SQL> CREATE TABLE Category (
  2  CategoryID INT NOT NULL PRIMARY KEY,
  3  DepartmentID INT NOT NULL,
  4  Name VARCHAR(50) NOT NULL,
  5  Description VARCHAR (200) NULL);
Table created.
SQL>
SQL> CREATE SEQUENCE CategoryIDSeq;
Sequence created.
SQL>
SQL> CREATE OR REPLACE TRIGGER CategoryAutonumberTrigger
  2  BEFORE INSERT ON Category
  3  FOR EACH ROW
  4  BEGIN
  5     SELECT CategoryIDSeq.NEXTVAL
  6     INTO :NEW.CategoryID FROM DUAL;
  7  END;
  8  /
Trigger created.
SQL> INSERT INTO Category (DepartmentID, Name, Description) VALUES (1, "Local", "In town");
1 row created.
SQL> INSERT INTO Category (DepartmentID, Name, Description) VALUES (1, "Remote", "Telecommute");
1 row created.
SQL> INSERT INTO Category (DepartmentID, Name, Description) VALUES (2, "Masks", "By bits");
1 row created.
SQL> INSERT INTO Category (DepartmentID, Name, Description) VALUES (3, "Wireless", "Not connected");
1 row created.
SQL> INSERT INTO Category (DepartmentID, Name, Description) VALUES (3, "Wired", "Connected");
1 row created.
SQL>
SQL>
SQL>
SQL> SELECT C.Name as "Category Name", Product.Name as "Product Name"
  2  FROM Product, Category C
  3  WHERE Product.ProductID IN
  4    (SELECT ProductID FROM ProductCategory
  5     WHERE ProductCategory.CategoryID = C.CategoryID)
  6  ORDER BY C.Name, Product.Name;
Category Name
--------------------------------------------------
Product Name
--------------------------------------------------
Local
PC
Local
Ruler
Masks
Desk
Masks
Keyboard
Masks
Pen
Masks
Ruler
Remote
Mouse
Wireless
Keyboard

8 rows selected.
SQL>
SQL>
SQL>
SQL> drop table Product;
Table dropped.
SQL> drop table ProductCategory;
Table dropped.
SQL> drop table Category;
Table dropped.
SQL> drop sequence CategoryIDSeq;
Sequence dropped.
SQL> drop sequence ProductIDSeq;
Sequence dropped.



How Many Products By Department with correlated subqueries 2

  
SQL>
SQL> CREATE TABLE Department (
  2  DepartmentID INT NOT NULL PRIMARY KEY,
  3  Name VARCHAR(50) NOT NULL,
  4  Description VARCHAR(200) NULL);
SQL>
SQL> CREATE SEQUENCE DepartmentIDSeq;
SQL>
SQL> CREATE OR REPLACE TRIGGER DepartmentAutonumberTrigger
  2  BEFORE INSERT ON Department
  3  FOR EACH ROW
  4  BEGIN
  5    SELECT DepartmentIDSeq.NEXTVAL
  6    INTO :NEW.DepartmentID FROM DUAL;
  7  END;
  8  /
SQL>
SQL> INSERT INTO Department (Name, Description)
  2     VALUES ("Software", "Coding");
SQL> INSERT INTO Department (Name, Description)
  2     VALUES ("Hardware", "Building");
SQL> INSERT INTO Department (Name, Description)
  2     VALUES ("QA", "Testing");
SQL>
SQL>
SQL>
SQL>
SQL> CREATE TABLE Category (
  2  CategoryID INT NOT NULL PRIMARY KEY,
  3  DepartmentID INT NOT NULL,
  4  Name VARCHAR(50) NOT NULL,
  5  Description VARCHAR (200) NULL);
SQL>
SQL> CREATE SEQUENCE CategoryIDSeq;
SQL>
SQL> CREATE OR REPLACE TRIGGER CategoryAutonumberTrigger
  2  BEFORE INSERT ON Category
  3  FOR EACH ROW
  4  BEGIN
  5     SELECT CategoryIDSeq.NEXTVAL
  6     INTO :NEW.CategoryID FROM DUAL;
  7  END;
  8  /
SQL> INSERT INTO Category (DepartmentID, Name, Description)
  2     VALUES (1, "Local", "In town");
SQL> INSERT INTO Category (DepartmentID, Name, Description)
  2     VALUES (1, "Remote", "Telecommute");
SQL> INSERT INTO Category (DepartmentID, Name, Description)
  2     VALUES (2, "Masks", "By bits");
SQL> INSERT INTO Category (DepartmentID, Name, Description)
  2     VALUES (3, "Wireless", "Not connected");
SQL> INSERT INTO Category (DepartmentID, Name, Description)
  2     VALUES (3, "Wired", "Connected");
SQL>
SQL>
SQL>
SQL>
SQL>
SQL> CREATE TABLE Product (
  2  ProductID INT NOT NULL PRIMARY KEY,
  3  Name VARCHAR(50) NOT NULL,
  4  Description VARCHAR(1000) NOT NULL,
  5  Price NUMBER NULL,
  6  ImagePath VARCHAR(50) NULL,
  7  soldout NUMBER(1,0) NULL,
  8  Promotion NUMBER(1,0) NULL);
SQL>
SQL> CREATE SEQUENCE ProductIDSeq;
SQL>
SQL> CREATE OR REPLACE TRIGGER ProductAutonumberTrigger
  2  BEFORE INSERT ON Product
  3  FOR EACH ROW
  4  BEGIN
  5     SELECT ProductIDSeq.NEXTVAL
  6     INTO :NEW.ProductID FROM DUAL;
  7  END;
  8  /
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath,soldout, Promotion)
  2  VALUES ("Pen", "Ball Pen",5.99, "pen.jpg", 1, 0);
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath,soldout, Promotion)
  2  VALUES ("Ruler","Long",14.99, "ruler.jpg", 0, 0);
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath,soldout, Promotion)
  2  VALUES ("Desk", "Computer Desk",5.99, "desk.jpg", 0, 1);
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("PC", "Notebook",49.99, "pc.jpg", 0, 1);
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("Mouse", "Wireless",9.99, "mouse.jpg",  1, 0);
SQL>
SQL> INSERT INTO Product (Name, Description, Price, ImagePath, soldout, Promotion)
  2  VALUES ("Keyboard","keyboard",3.75, "keyboard.jpg", 0, 0);
SQL>
SQL>
SQL> CREATE TABLE ProductCategory (
  2  ProductID INT NOT NULL,
  3  CategoryID INT NOT NULL,
  4  PRIMARY KEY (ProductID, CategoryID)
  5  );
SQL>
SQL>
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (1,3);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (2,1);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (2,3);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (3,3);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (4,1);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (5,2);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (6,3);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (6,4);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (7,4);
SQL> INSERT INTO ProductCategory (ProductID, CategoryID) VALUES (8,5);
SQL>
SQL> SELECT D.Name AS "Department",
  2       (SELECT COUNT(ProductID)
  3        FROM ProductCategory INNER JOIN Category
  4        ON ProductCategory.CategoryID = Category.CategoryID
  5        WHERE Category.DepartmentID = D.DepartmentID) AS "Products"
  6  FROM Department D;
Software
         3
Hardware
         4
QA
         3
SQL>
SQL>
SQL>
SQL>
SQL> SELECT D.Name AS "Department", COUNT(P.Name) AS "Products"
  2  FROM Department D, Product P
  3  WHERE ProductID IN
  4       (SELECT ProductID
  5        FROM ProductCategory INNER JOIN Category
  6        ON ProductCategory.CategoryID = Category.CategoryID
  7        WHERE Category.DepartmentID = D.DepartmentID)
  8  GROUP BY D.Name
  9  ORDER BY D.Name;
Hardware
         4
QA
         1
Software
         3
SQL>
SQL>
SQL> drop table department;
SQL> drop sequence DepartmentIDSeq;
SQL> drop table Product;
SQL> drop table ProductCategory;
SQL> drop table Category;
SQL> drop sequence CategoryIDSeq;
SQL> drop sequence ProductIDSeq;



Inner query Demo

   
SQL>
SQL> create table t
  2  as
  3  select object_name ename,
  4         mod(object_id,50) deptno,
  5         object_id sal
  6    from all_objects
  7   where rownum <= 1000
  8  /
Table created.
SQL>
SQL>
SQL>
SQL> select deptno, ename, sal
  2  from t e1
  3  where (select count(*)
  4         from t e2
  5         where e2.deptno = e1.deptno
  6         and e2.sal >= e1.sal) <= 3
  7  order by deptno, sal desc
  8  /
DEPTNO ENAME                               SAL
------ ------------------------------ --------
     0 V_$LOCK                         1050.00
       V_$BUFFER_POOL_STATISTICS       1000.00
       V_$DLM_ALL_LOCKS                 950.00
     1 V$LOCK                          1051.00
       V$BUFFER_POOL_STATISTICS        1001.00
       V$DLM_ALL_LOCKS                  951.00
     2 V_$SESSTAT                      1052.00
       V_$INSTANCE_RECOVERY            1002.00
       V_$DLM_LOCKS                     952.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
     3 V$SESSTAT                       1053.00
       V$INSTANCE_RECOVERY             1003.00
       V$DLM_LOCKS                      953.00
     4 V_$MYSTAT                       1054.00
       V_$CONTROLFILE                  1004.00
       V_$DLM_RESS                      954.00
     5 V$MYSTAT                        1055.00
       V$CONTROLFILE                   1005.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
     5 V$DLM_RESS                       955.00
     6 V_$SUBCACHE                     1056.00
       V_$LOG                          1006.00
       V_$HVMASTER_INFO                 956.00
     7 V$SUBCACHE                      1057.00
       V$LOG                           1007.00
       V$HVMASTER_INFO                  957.00
     8 V_$SYSSTAT                      1058.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
     8 V_$STANDBY_LOG                  1008.00
       V_$GCSHVMASTER_INFO              958.00
     9 V$SYSSTAT                       1059.00
       V$STANDBY_LOG                   1009.00
       V$GCSHVMASTER_INFO               959.00
    10 V_$STATNAME                     1060.00
       V_$DATAGUARD_STATUS             1010.00
       V_$GCSPFMASTER_INFO              960.00

DEPTNO ENAME                               SAL
------ ------------------------------ --------
    11 V$STATNAME                      1061.00
       V$DATAGUARD_STATUS              1011.00
       V$GCSPFMASTER_INFO               961.00
    12 V_$OSSTAT                       1062.00
       V_$THREAD                       1012.00
       GV_$DLM_TRAFFIC_CONTROLLER       962.00
    13 V$OSSTAT                        1063.00
       V$THREAD                        1013.00
       GV$DLM_TRAFFIC_CONTROLLER        963.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    14 V_$ACCESS                       1064.00
       V_$PROCESS                      1014.00
       V_$DLM_TRAFFIC_CONTROLLER        964.00
    15 V$ACCESS                        1065.00
       V$PROCESS                       1015.00
       V$DLM_TRAFFIC_CONTROLLER         965.00
    16 V_$OBJECT_DEPENDENCY            1066.00
       V_$BGPROCESS                    1016.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    16 V_$GES_ENQUEUE                   966.00
    17 V$OBJECT_DEPENDENCY             1067.00
       V$BGPROCESS                     1017.00
       V$GES_ENQUEUE                    967.00
    18 V_$DBFILE                       1068.00
       V_$SESSION                      1018.00
       V_$GES_BLOCKING_ENQUEUE          968.00
    19 V$DBFILE                        1069.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    19 V$SESSION                       1019.00
       V$GES_BLOCKING_ENQUEUE           969.00
    20 V_$FILESTAT                     1070.00
       V_$LICENSE                      1020.00
       V_$GC_ELEMENT                    970.00
    21 V$FILESTAT                      1071.00
       V$LICENSE                       1021.00
       V$GC_ELEMENT                     971.00

DEPTNO ENAME                               SAL
------ ------------------------------ --------
    22 V_$TEMPSTAT                     1072.00
       V_$TRANSACTION                  1022.00
       V_$CR_BLOCK_SERVER               972.00
    23 V$TEMPSTAT                      1073.00
       V$TRANSACTION                   1023.00
       V$CR_BLOCK_SERVER                973.00
    24 V_$LOGFILE                      1074.00
       V_$BSP                          1024.00
       V_$CURRENT_BLOCK_SERVER          974.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    25 V$LOGFILE                       1075.00
       V$BSP                           1025.00
       V$CURRENT_BLOCK_SERVER           975.00
    26 V_$FLASHBACK_DATABASE_LOGFILE   1076.00
       V_$FAST_START_SERVERS           1026.00
       V_$GC_ELEMENTS_W_COLLISIONS      976.00
    27 V$FLASHBACK_DATABASE_LOGFILE    1077.00
       V$FAST_START_SERVERS            1027.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    27 V$GC_ELEMENTS_WITH_COLLISIONS    977.00
    28 V_$FLASHBACK_DATABASE_LOG       1078.00
       V_$FAST_START_TRANSACTIONS      1028.00
       V_$FILE_CACHE_TRANSFER           978.00
    29 V$FLASHBACK_DATABASE_LOG        1079.00
       V$FAST_START_TRANSACTIONS       1029.00
       V$FILE_CACHE_TRANSFER            979.00
    30 V_$FLASHBACK_DATABASE_STAT      1080.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    30 V_$LOCKED_OBJECT                1030.00
       V_$TEMP_CACHE_TRANSFER           980.00
    31 V$FLASHBACK_DATABASE_STAT       1081.00
       V$LOCKED_OBJECT                 1031.00
       V$TEMP_CACHE_TRANSFER            981.00
    32 V_$RESTORE_POINT                1082.00
       V_$LATCH                        1032.00
       V_$CLASS_CACHE_TRANSFER          982.00

DEPTNO ENAME                               SAL
------ ------------------------------ --------
    33 V$RESTORE_POINT                 1083.00
       V$LATCH                         1033.00
       V$CLASS_CACHE_TRANSFER           983.00
    34 V_$ROLLNAME                     1084.00
       V_$LATCH_CHILDREN               1034.00
       V_$BH                            984.00
    35 V$ROLLNAME                      1085.00
       V$LATCH_CHILDREN                1035.00
       V$BH                             985.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    36 V_$ROLLSTAT                     1086.00
       V_$LATCH_PARENT                 1036.00
       V_$LOCK_ELEMENT                  986.00
    37 V$ROLLSTAT                      1087.00
       V$LATCH_PARENT                  1037.00
       V$LOCK_ELEMENT                   987.00
    38 V_$UNDOSTAT                     1088.00
       V_$LATCHNAME                    1038.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    38 V_$LOCKS_WITH_COLLISIONS         988.00
    39 V$UNDOSTAT                      1089.00
       V$LATCHNAME                     1039.00
       V$LOCKS_WITH_COLLISIONS          989.00
    40 V_$SGA                          1090.00
       V_$LATCHHOLDER                  1040.00
       V_$FILE_PING                     990.00
    41 V$LATCHHOLDER                   1041.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    41 V$FILE_PING                      991.00
       V$SQL_OPTIMIZER_ENV              941.00
    42 V_$LATCH_MISSES                 1042.00
       V_$TEMP_PING                     992.00
       V_$DLM_MISC                      942.00
    43 V$LATCH_MISSES                  1043.00
       V$TEMP_PING                      993.00
       V$DLM_MISC                       943.00

DEPTNO ENAME                               SAL
------ ------------------------------ --------
    44 V_$SESSION_LONGOPS              1044.00
       V_$CLASS_PING                    994.00
       V_$DLM_LATCH                     944.00
    45 V$SESSION_LONGOPS               1045.00
       V$CLASS_PING                     995.00
       V$DLM_LATCH                      945.00
    46 V_$RESOURCE                     1046.00
       V_$INSTANCE_CACHE_TRANSFER       996.00
       V_$DLM_CONVERT_LOCAL             946.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    47 V$RESOURCE                      1047.00
       V$INSTANCE_CACHE_TRANSFER        997.00
       V$DLM_CONVERT_LOCAL              947.00
    48 V_$_LOCK                        1048.00
       V_$BUFFER_POOL                   998.00
       V_$DLM_CONVERT_REMOTE            948.00
    49 V$_LOCK                         1049.00
       V$BUFFER_POOL                    999.00
DEPTNO ENAME                               SAL
------ ------------------------------ --------
    49 V$DLM_CONVERT_REMOTE             949.00

150 rows selected.
SQL>
SQL> drop table t;
Table dropped.
SQL>



To delete the records of emps whose salary is below the average salary in the department (correlated subquery):

  
SQL>
SQL>
SQL>
SQL> CREATE TABLE EMP(
  2      EMPNO NUMBER(4) NOT NULL,
  3      ENAME VARCHAR2(10),
  4      JOB VARCHAR2(9),
  5      MGR NUMBER(4),
  6      HIREDATE DATE,
  7      SAL NUMBER(7, 2),
  8      COMM NUMBER(7, 2),
  9      DEPTNO NUMBER(2)
 10  );
Table created.

SQL> INSERT INTO EMP VALUES(2, "Jack", "Tester", 6,TO_DATE("20-FEB-1981", "DD-MON-YYYY"), 1600, 300, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(3, "Wil", "Tester", 6,TO_DATE("22-FEB-1981", "DD-MON-YYYY"), 1250, 500, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(4, "Jane", "Designer", 9,TO_DATE("2-APR-1981", "DD-MON-YYYY"), 2975, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES(5, "Mary", "Tester", 6,TO_DATE("28-SEP-1981", "DD-MON-YYYY"), 1250, 1400, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(6, "Black", "Designer", 9,TO_DATE("1-MAY-1981", "DD-MON-YYYY"), 2850, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(7, "Chris", "Designer", 9,TO_DATE("9-JUN-1981", "DD-MON-YYYY"), 2450, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES(8, "Smart", "Helper", 4,TO_DATE("09-DEC-1982", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES(9, "Peter", "Manager", NULL,TO_DATE("17-NOV-1981", "DD-MON-YYYY"), 5000, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES(10, "Take", "Tester", 6,TO_DATE("8-SEP-1981", "DD-MON-YYYY"), 1500, 0, 30);
1 row created.

SQL> INSERT INTO EMP VALUES(13, "Fake", "Helper", 4,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.

SQL>
SQL> DELETE FROM emp e
  2      WHERE sal < (SELECT AVG(sal) FROM emp
  3                      WHERE  deptno = e.deptno);
6 rows deleted.
SQL>
SQL> drop table emp;
Table dropped.



To update the salary of all emps to the maximum salary in the corresponding department (correlated subquery):

  
SQL>
SQL>
SQL> CREATE TABLE EMP(
  2      EMPNO NUMBER(4) NOT NULL,
  3      ENAME VARCHAR2(10),
  4      JOB VARCHAR2(9),
  5      MGR NUMBER(4),
  6      HIREDATE DATE,
  7      SAL NUMBER(7, 2),
  8      COMM NUMBER(7, 2),
  9      DEPTNO NUMBER(2)
 10  );
Table created.

SQL> INSERT INTO EMP VALUES(2, "Jack", "Tester", 6,TO_DATE("20-FEB-1981", "DD-MON-YYYY"), 1600, 300, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(3, "Wil", "Tester", 6,TO_DATE("22-FEB-1981", "DD-MON-YYYY"), 1250, 500, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(4, "Jane", "Designer", 9,TO_DATE("2-APR-1981", "DD-MON-YYYY"), 2975, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES(5, "Mary", "Tester", 6,TO_DATE("28-SEP-1981", "DD-MON-YYYY"), 1250, 1400, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(6, "Black", "Designer", 9,TO_DATE("1-MAY-1981", "DD-MON-YYYY"), 2850, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES(7, "Chris", "Designer", 9,TO_DATE("9-JUN-1981", "DD-MON-YYYY"), 2450, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES(8, "Smart", "Helper", 4,TO_DATE("09-DEC-1982", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES(9, "Peter", "Manager", NULL,TO_DATE("17-NOV-1981", "DD-MON-YYYY"), 5000, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES(10, "Take", "Tester", 6,TO_DATE("8-SEP-1981", "DD-MON-YYYY"), 1500, 0, 30);
1 row created.

SQL> INSERT INTO EMP VALUES(13, "Fake", "Helper", 4,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.

SQL>
SQL>
SQL> UPDATE emp
  2      SET    sal = (SELECT MAX(sal)
  3                       FROM   emp e
  4                       WHERE  e.deptno = emp.deptno);
10 rows updated.
SQL>
SQL> drop table emp;
Table dropped.



Using EXISTS with a Correlated Subquery

  

SQL> CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
  2                    ENAME VARCHAR2(10),
  3                    JOB VARCHAR2(9),
  4                    MGR NUMBER(4),
  5                    HIREDATE DATE,
  6                    SAL NUMBER(7, 2),
  7                    COMM NUMBER(7, 2),
  8                    DEPTNO NUMBER(2));
Table created.
SQL>
SQL> INSERT INTO EMP VALUES (7369, "SMITH", "CLERK",    7902, TO_DATE("17-DEC-1980", "DD-MON-YYYY"), 800, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7499, "ALLEN", "SALESMAN", 7698, TO_DATE("20-FEB-1981", "DD-MON-YYYY"), 1600, 300, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7521, "WARD",  "SALESMAN", 7698, TO_DATE("22-FEB-1981", "DD-MON-YYYY"), 1250, 500, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7566, "JONES", "MANAGER",  7839, TO_DATE("2-APR-1981",  "DD-MON-YYYY"), 2975, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7654, "MARTIN", "SALESMAN", 7698,TO_DATE("28-SEP-1981", "DD-MON-YYYY"), 1250, 1400, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7698, "BLAKE", "MANAGER", 7839,TO_DATE("1-MAY-1981", "DD-MON-YYYY"), 2850, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7782, "CLARK", "MANAGER", 7839,TO_DATE("9-JUN-1981", "DD-MON-YYYY"), 2450, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES (7788, "SCOTT", "ANALYST", 7566,TO_DATE("09-DEC-1982", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7839, "KING", "PRESIDENT", NULL,TO_DATE("17-NOV-1981", "DD-MON-YYYY"), 5000, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES (7844, "TURNER", "SALESMAN", 7698,TO_DATE("8-SEP-1981", "DD-MON-YYYY"), 1500, 0, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7876, "ADAMS", "CLERK", 7788,TO_DATE("12-JAN-1983", "DD-MON-YYYY"), 1100, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7900, "JAMES", "CLERK", 7698,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 950, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7902, "FORD", "ANALYST", 7566,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7934, "MILLER", "CLERK", 7782,TO_DATE("23-JAN-1982", "DD-MON-YYYY"), 1300, NULL, 10);
1 row created.
SQL>
SQL> select * from emp;
     EMPNO ENAME      JOB              MGR HIREDATE           SAL       COMM     DEPTNO
---------- ---------- --------- ---------- ----------- ---------- ---------- ----------
      7369 SMITH      CLERK           7902 1980-DEC-17        800                    20
      7499 ALLEN      SALESMAN        7698 1981-FEB-20       1600        300         30
      7521 WARD       SALESMAN        7698 1981-FEB-22       1250        500         30
      7566 JONES      MANAGER         7839 1981-APR-02       2975                    20
      7654 MARTIN     SALESMAN        7698 1981-SEP-28       1250       1400         30
      7698 BLAKE      MANAGER         7839 1981-MAY-01       2850                    30
      7782 CLARK      MANAGER         7839 1981-JUN-09       2450                    10
      7788 SCOTT      ANALYST         7566 1982-DEC-09       3000                    20
      7839 KING       PRESIDENT            1981-NOV-17       5000                    10
      7844 TURNER     SALESMAN        7698 1981-SEP-08       1500          0         30
      7876 ADAMS      CLERK           7788 1983-JAN-12       1100                    20
      7900 JAMES      CLERK           7698 1981-DEC-03        950                    30
      7902 FORD       ANALYST         7566 1981-DEC-03       3000                    20
      7934 MILLER     CLERK           7782 1982-JAN-23       1300                    10
14 rows selected.
SQL>
SQL> --Using EXISTS with a Correlated Subquery
SQL>
SQL> SELECT empno, ename
  2  FROM emp outer
  3  WHERE EXISTS
  4    (SELECT empno
  5     FROM emp inner
  6     WHERE inner.mgr = outer.empno);
     EMPNO ENAME
---------- ----------
      7902 FORD
      7698 BLAKE
      7839 KING
      7566 JONES
      7788 SCOTT
      7782 CLARK
6 rows selected.
SQL>
SQL> drop table emp;
Table dropped.
SQL>
SQL>



Using NOT EXISTS with a Correlated Subquery

  

SQL> CREATE TABLE EMP (EMPNO NUMBER(4) NOT NULL,
  2                    ENAME VARCHAR2(10),
  3                    JOB VARCHAR2(9),
  4                    MGR NUMBER(4),
  5                    HIREDATE DATE,
  6                    SAL NUMBER(7, 2),
  7                    COMM NUMBER(7, 2),
  8                    DEPTNO NUMBER(2));
Table created.
SQL>
SQL> INSERT INTO EMP VALUES (7369, "SMITH", "CLERK",    7902, TO_DATE("17-DEC-1980", "DD-MON-YYYY"), 800, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7499, "ALLEN", "SALESMAN", 7698, TO_DATE("20-FEB-1981", "DD-MON-YYYY"), 1600, 300, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7521, "WARD",  "SALESMAN", 7698, TO_DATE("22-FEB-1981", "DD-MON-YYYY"), 1250, 500, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7566, "JONES", "MANAGER",  7839, TO_DATE("2-APR-1981",  "DD-MON-YYYY"), 2975, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7654, "MARTIN", "SALESMAN", 7698,TO_DATE("28-SEP-1981", "DD-MON-YYYY"), 1250, 1400, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7698, "BLAKE", "MANAGER", 7839,TO_DATE("1-MAY-1981", "DD-MON-YYYY"), 2850, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7782, "CLARK", "MANAGER", 7839,TO_DATE("9-JUN-1981", "DD-MON-YYYY"), 2450, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES (7788, "SCOTT", "ANALYST", 7566,TO_DATE("09-DEC-1982", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7839, "KING", "PRESIDENT", NULL,TO_DATE("17-NOV-1981", "DD-MON-YYYY"), 5000, NULL, 10);
1 row created.
SQL> INSERT INTO EMP VALUES (7844, "TURNER", "SALESMAN", 7698,TO_DATE("8-SEP-1981", "DD-MON-YYYY"), 1500, 0, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7876, "ADAMS", "CLERK", 7788,TO_DATE("12-JAN-1983", "DD-MON-YYYY"), 1100, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7900, "JAMES", "CLERK", 7698,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 950, NULL, 30);
1 row created.
SQL> INSERT INTO EMP VALUES (7902, "FORD", "ANALYST", 7566,TO_DATE("3-DEC-1981", "DD-MON-YYYY"), 3000, NULL, 20);
1 row created.
SQL> INSERT INTO EMP VALUES (7934, "MILLER", "CLERK", 7782,TO_DATE("23-JAN-1982", "DD-MON-YYYY"), 1300, NULL, 10);
1 row created.
SQL>
SQL> select * from emp;
     EMPNO ENAME      JOB              MGR HIREDATE           SAL       COMM     DEPTNO
---------- ---------- --------- ---------- ----------- ---------- ---------- ----------
      7369 SMITH      CLERK           7902 1980-DEC-17        800                    20
      7499 ALLEN      SALESMAN        7698 1981-FEB-20       1600        300         30
      7521 WARD       SALESMAN        7698 1981-FEB-22       1250        500         30
      7566 JONES      MANAGER         7839 1981-APR-02       2975                    20
      7654 MARTIN     SALESMAN        7698 1981-SEP-28       1250       1400         30
      7698 BLAKE      MANAGER         7839 1981-MAY-01       2850                    30
      7782 CLARK      MANAGER         7839 1981-JUN-09       2450                    10
      7788 SCOTT      ANALYST         7566 1982-DEC-09       3000                    20
      7839 KING       PRESIDENT            1981-NOV-17       5000                    10
      7844 TURNER     SALESMAN        7698 1981-SEP-08       1500          0         30
      7876 ADAMS      CLERK           7788 1983-JAN-12       1100                    20
      7900 JAMES      CLERK           7698 1981-DEC-03        950                    30
      7902 FORD       ANALYST         7566 1981-DEC-03       3000                    20
      7934 MILLER     CLERK           7782 1982-JAN-23       1300                    10
14 rows selected.
SQL>
SQL> --Using NOT EXISTS with a Correlated Subquery
SQL>
SQL> SELECT empno, ename
  2  FROM emp outer
  3  WHERE NOT EXISTS
  4    (SELECT 1
  5     FROM emp inner
  6     WHERE inner.mgr = outer.empno);
     EMPNO ENAME
---------- ----------
      7844 TURNER
      7521 WARD
      7654 MARTIN
      7499 ALLEN
      7934 MILLER
      7369 SMITH
      7876 ADAMS
      7900 JAMES
8 rows selected.
SQL>
SQL>
SQL> drop table emp;
Table dropped.
SQL>
SQL>