Oracle PL/SQL/Select Query/Null Value Concatanation
Column format: default value for null value
<source lang="sql">
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.
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Oracle converts the null into a blank text string
<source lang="sql">
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>
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