Oracle PL/SQL/Select Query/Null Value Concatanation

Column format: default value for null value

 
SQL> create table registrations
  2  ( attendee    NUMBER(4)
  3  , course      VARCHAR2(6)
  4  , begindate   DATE
  5  , evaluation  NUMBER(1)
  6  , constraint  R_PK        primary key(attendee,course,begindate)
  7  ) ;
Table created.
SQL>
SQL> insert into registrations values (2,"SQL",date "2009-04-12",4   );
1 row created.
SQL> insert into registrations values (14,"SQL",date "2009-04-12",5   );
1 row created.
SQL> insert into registrations values (6,"SQL",date "2009-04-12",4   );
1 row created.
SQL> insert into registrations values (11,"SQL",date "2009-04-12",2   );
1 row created.
SQL> insert into registrations values (8,"SQL",date "2009-10-04",NULL);
1 row created.
SQL> insert into registrations values (9,"SQL",date "2009-10-04",3   );
1 row created.
SQL> insert into registrations values (13,"SQL",date "2009-10-04",4   );
1 row created.
SQL> insert into registrations values (13,"SQL",date "2009-12-13",NULL);
1 row created.
SQL> insert into registrations values (6,"SQL",date "2009-12-13",NULL);
1 row created.
SQL> insert into registrations values (3,"OAU",date "2009-08-10",4   );
1 row created.
SQL> insert into registrations values (12,"OAU",date "2009-08-10",4   );
1 row created.
SQL> insert into registrations values (13,"OAU",date "2009-08-10",5   );
1 row created.
SQL>
SQL> column evaluation NULL "unknown!!!"
SQL>
SQL> select * from registrations
  2  where  attendee = 4;
no rows selected
SQL>
SQL>
SQL> drop table registrations;
Table dropped.

Oracle converts the null into a blank text string

 

SQL>
SQL>
SQL> -- create demo table
SQL> create table Employee(
  2    ID                 VARCHAR2(4 BYTE)         NOT NULL,
  3    First_Name         VARCHAR2(10 BYTE),
  4    Last_Name          VARCHAR2(10 BYTE),
  5    Start_Date         DATE,
  6    End_Date           DATE,
  7    Salary             Number(8,2),
  8    City               VARCHAR2(10 BYTE),
  9    Description        VARCHAR2(15 BYTE)
 10  )
 11  /
Table created.
SQL>
SQL> -- prepare data
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2               values ("01","Jason",    "Martin",  to_date("19960725","YYYYMMDD"), to_date("20060725","YYYYMMDD"), 1234.56, "Toronto",  "Programmer")
  3  /
1 row created.
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("02","Alison",   "Mathews", to_date("19760321","YYYYMMDD"), to_date("19860221","YYYYMMDD"), 2334.78, "Vancouver","Tester")
  3  /
1 row created.
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("03","James",    "Smith",   to_date("19781212","YYYYMMDD"), to_date("19900315","YYYYMMDD"), 2334.78, "Vancouver","Tester")
  3  /
1 row created.
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("04","Celia",    "Rice",    to_date("19821024","YYYYMMDD"), to_date("19990421","YYYYMMDD"), 2334.78, "Vancouver","Manager")
  3  /
1 row created.
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary,  City,       Description)
  2                values("05","Robert",   "Black",   to_date("19840115","YYYYMMDD"), to_date("19980808","YYYYMMDD"), 2334.78, "Vancouver","Tester")
  3  /
1 row created.
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values("06","Linda",    "Green",   to_date("19870730","YYYYMMDD"), to_date("19960104","YYYYMMDD"), 2334.78,"New York",  "Tester")
  3  /
1 row created.
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values("07","David",    "Larry",   to_date("19901231","YYYYMMDD"), to_date("19980212","YYYYMMDD"), 2334.78,"New York",  "Manager")
  3  /
1 row created.
SQL> insert into Employee(ID,  First_Name, Last_Name, Start_Date,                     End_Date,                       Salary, City,        Description)
  2                values("08","James",    "Cat",     to_date("19960917","YYYYMMDD"), to_date("20020415","YYYYMMDD"), 2334.78,"Vancouver", "Tester")
  3  /
1 row created.
SQL>
SQL>
SQL>
SQL> -- display data in the table
SQL> select * from Employee
  2  /
ID   FIRST_NAME LAST_NAME  START_DAT END_DATE      SALARY CITY       DESCRIPTION
---- ---------- ---------- --------- --------- ---------- ---------- ---------------
01   Jason      Martin     25-JUL-96 25-JUL-06    1234.56 Toronto    Programmer
02   Alison     Mathews    21-MAR-76 21-FEB-86    2334.78 Vancouver  Tester
03   James      Smith      12-DEC-78 15-MAR-90    2334.78 Vancouver  Tester
04   Celia      Rice       24-OCT-82 21-APR-99    2334.78 Vancouver  Manager
05   Robert     Black      15-JAN-84 08-AUG-98    2334.78 Vancouver  Tester
06   Linda      Green      30-JUL-87 04-JAN-96    2334.78 New York   Tester
07   David      Larry      31-DEC-90 12-FEB-98    2334.78 New York   Manager
08   James      Cat        17-SEP-96 15-APR-02    2334.78 Vancouver  Tester
8 rows selected.
SQL>
SQL>
SQL>
SQL>
SQL>
SQL> -- Oracle converts the null into a blank text string.
SQL>
SQL> SELECT ID, First_Name || NULL  FROM Employee;
ID   FIRST_NAME
---- ----------
01   Jason
02   Alison
03   James
04   Celia
05   Robert
06   Linda
07   David
08   James
8 rows selected.
SQL>
SQL>
SQL>
SQL>
SQL>
SQL>
SQL>
SQL>
SQL> -- clean the table
SQL> drop table Employee
  2  /
Table dropped.
SQL>
SQL>
SQL>