Update statement using case

Question

Hello my friends
I have one table "encompasses": continent,country,percentage
now the update should change the continent field, all "Europe" to "Asia" and all "Asia" to "America" and "America" to "Europe" by using case and just one update statement.
I wrote so and i got this error
Error starting at line 2 in command:
UPDATE encompasses
   SET continent=    
      CASE  WHEN continent='Europe'  THEN 'Asia'  
      WHEN continent='Asia'  THEN 'America' 
      WHEN continent='America' THEN 'Europe'
      END
Error report:
SQL Error: ORA-01407: cannot update ("intern"."ENCOMPASSES"."CONTINENT") to NULL
01407. 00000 -  "cannot update (%s) to NULL"
*Cause:   
*Action:please give me hints,thank u.
--  File created - Monday-May-13-2013  
  CREATE TABLE "intern"."ENCOMPASSES" ("COUNTRY" CHAR(2), "CONTINENT" VARCHAR2(20), "PERCENTAGE" NUMBER)
   COMMENT ON COLUMN "intern"."ENCOMPASSES"."COUNTRY" IS 'the country code'
   COMMENT ON COLUMN "intern"."ENCOMPASSES"."CONTINENT" IS 'the continent name'
   COMMENT ON COLUMN "intern"."ENCOMPASSES"."PERCENTAGE" IS 'percentage, how much of the area of a country belongs to the
            continent'
   COMMENT ON TABLE "intern"."ENCOMPASSES"  IS 'information to which continents a country belongs'
REM INSERTING into intern.ENCOMPASSES
SET DEFINE OFF;
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('cx','Asia',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('eg','Asia',10);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('ge','Asia',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('id','Asia',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('ad','Europe',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('al','Europe',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('at','Europe',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('ba','Europe',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('pa','America',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('pe','America',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('pm','America',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('pr','America',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('py','America',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('sr','America',100);
Insert into intern.ENCOMPASSES (COUNTRY,CONTINENT,PERCENTAGE) values ('sv','America',100);thank you, im using oracle 11g and ubuntu12
best,david
Edited by: 1003209 on 13-May-2013 10:12

Answer 1

1003209 wrote:
Hello my friends
I have one table "encompasses": continent,country,percentage
now the update should change the continent field, all "Europe" to "Asia" and all "Asia" to "America" and "America" to "Europe" by using case and just one update statement.
I wrote so and i got this error
Error starting at line 2 in command:
UPDATE encompasses
    SET continent=    
       CASE  WHEN continent='Europe'  THEN 'Asia'  
       WHEN continent='Asia'  THEN 'America' 
       WHEN continent='America' THEN 'Europe'
       END
Error report:
SQL Error: ORA-01407: cannot update ("intern"."ENCOMPASSES"."CONTINENT") to NULL
01407. 00000 -  "cannot update (%s) to NULL"
*Cause:   
*Action:This seems the column Continent has not null contraint on it, hence when there is a continent other than the three you mentioned above the case statement is evaluating it to null and hence failing e.g. if there is a record with continent = 'Antartica' it will try to update that as null.
so either add this:
WHERE continent in ('Europe' ,'Asia','America')this will update only for this continents and ignore other values.
If you want to update other continents as well then have a else condition in CASE statement to assign defualt value.
Regards,
Santosh