CASE STATEMENTS AND CASE EXPRESSIONS IN ORACLE9I PL/SQL

Question

제품 : PL/SQL
작성날짜 : 2001-11-13
CASE STATEMENTS AND CASE EXPRESSIONS IN ORACLE9I PL/SQL
=======================================================
PURPOSE
아래의 자료는 Case 문에서 oracle 8.1.7과 Oracle 9i의 New Feature로 8.1.7에서는
sqlplus 에서만 가능했고, 9i 부터는 pl/sql 까지 가능하다.
Explanation
1. Oracle 8.1.7 Feature
Oracle 8.1.7 에서 Case 문은 Decode 문과 유사하지만, 기존의 decode 문을 쓰는 것보다
더 많은 확장성과 Logical Power와 좋은 성능을 제공한다. 주로 나이와 같이 category 별로
나눌때 주로 사용하고 Syntex는 아래와 같다.
CASE WHEN <cond1> THEN <v1> WHEN <cond2> THEN <v2> ... [ELSE <vn+1> ] END
각각의 WHEN...THEN 절의 argument 는 255 까지 가능하고 이 Limit를 해결하려면
Oracle 8i Reference를 참조하면 된다.
The maximum number of arguments in a CASE expression is 255, and each
WHEN ... THEN pair counts as two arguments. To avoid exceeding the limit of 128 choices,
you can nest CASE expressions. That is expr1 can itself be a CASE expression.
Case Example : 한 회사의 모든 종업원의 평균 봉급을 계산하는데 봉급이 $2000보다 작은경우
2000으로 계산을 하는 방법이 pl/sql을 대신하여 case function을 사용할 수 있다.
SELECT AVG(CASE when e.sal > 2000 THEN e.sal ELSE 2000 end) FROM emp e;
Case Example : 나이를 column으로 가지고 있는 customer table을 예로 들어보자.
SQL> SELECT
2 SUM(CASE WHEN age BETWEEN 70 AND 79 THEN 1 ELSE 0 END) as "70-79",
3 SUM(CASE WHEN age BETWEEN 80 AND 89 THEN 1 ELSE 0 END) as "80-89",
4 SUM(CASE WHEN age BETWEEN 90 AND 99 THEN 1 ELSE 0 END) as "90-99",
5 SUM(CASE WHEN age > 99 THEN 1 ELSE 0 END) as "100+"
6 FROM customer;
70-79 80-89 90-99 100+
4 2 3 1
1 SELECT
2 (CASE WHEN age BETWEEN 70 AND 79 THEN '70-79'
3 WHEN age BETWEEN 80 and 89 THEN '80-89'
4 WHEN age BETWEEN 90 and 99 THEN '90-99'
5 WHEN age > 99 THEN '100+' END) as age_group,
6 COUNT(*) as age_count
7 FROM customer
8 GROUP BY
9 (CASE WHEN age BETWEEN 70 AND 79 THEN '70-79'
10 WHEN age BETWEEN 80 and 89 THEN '80-89'
11 WHEN age BETWEEN 90 and 99 THEN '90-99'
12* WHEN age > 99 THEN '100+' END)
SQL> /
AGE_G AGE_COUNT
100+ 1
70-79 4
80-89 2
90-99 3
Example
2. Oracle 9i Feature
Oracle 9i부터는 pl/sql에서도 case문을 사용할 수 있으면 이것은
복잡한 if-else 구문을 없애고, C언어의 switch문과 같은 기능을 한다.
아래의 9i pl/sql Sample 및 제약 사항을 보면 아래와 같다.
Sample 1:
A simple example demonstrating the proper syntax for a case
statement
using a character variable as the selector. See the section entitled
'Restrictions' at the end of this article for details on which PLSQL
datatypes may appear as a selector in a case statement or
expression.
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set serveroutput on
declare
achar char(1) := '&achar';
begin
case achar
when 'A' then dbms_output.put_line('The description was Excellent');
when 'B' then dbms_output.put_line('The description was Very Good');
when 'C' then dbms_output.put_line('The description was Good');
when 'D' then dbms_output.put_line('The description was Fair');
when 'F' then dbms_output.put_line('The description was Poor');
else dbms_output.put_line('The description was No such Grade');
end case;
end;
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Sample 2:
A simple example demonstrating the proper syntax for a case
expression
using a character variable as the selector. See the section entitled
'Restrictions' at the end of this article for details on which PLSQL
datatypes may appear as a selector in a case statement or
expression.
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set serveroutput on
declare
achar char(1) := '&achar';
description varchar2(20);
begin
description :=
case achar
when 'A' then 'Excellent'
when 'B' then 'Very Good'
when 'C' then 'Good'
when 'D' then 'Fair'
when 'F' then 'Poor'
else 'No such grade'
end;
dbms_output.put_line('The description was ' || description);
end;
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NOTE: The above simple samples demonstrate two subtle differences in the
syntax
required for case statements and expressions.
1) A case STATEMENT is terminated using the 'end case' keywords; a
case
EXPRESSION is terminated using only the 'end' keyword.
2) Each item in a case STATEMENT consists of one or more
statements, each
terminated by a semicolon. Each item in a case expression
consists of
exactly one expression, not terminated by a semicolon.
Sample 3:
Sample 1 demonstrates a simple case statement in which the selector
is
compared for equality with each item in the case statement body.
PL/SQL
also provides a 'searched' case statement as an alternative; rather
than
providing a selector and a list of values, each item in the body of
the
case statement provides its own predicate. This predicate can be any
valid boolean expression, but only one case will be selected.
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set serveroutput on
declare
achar char(1) := '&achar';
begin
case
when achar = 'A' then dbms_output.put_line('The description was
Excellent');
when achar = 'B' then dbms_output.put_line('The description was Very
Good');
when achar = 'C' then dbms_output.put_line('The description was
Good');
when achar = 'D' then dbms_output.put_line('The description was
Fair');
when achar = 'F' then dbms_output.put_line('The description was
Poor');
else dbms_output.put_line('The description was No such Grade');
end case;
end;
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Sample 4:
This sample demonstrates the proper syntax for a case expression of
the
type discussed in Sample 3 above.
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set serveroutput on
declare
achar char(1) := '&achar';
description varchar2(20);
begin
description :=
case
when achar = 'A' then 'Excellent'
when achar = 'B' then 'Very Good'
when achar = 'C' then 'Good'
when achar = 'D' then 'Fair'
when achar = 'F' then 'Poor'
else 'No such grade'
end;
dbms_output.put_line('The description was ' || description);
end;
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Sample 5:
This sample demonstrates the use of nested case statements. It is
also
permissable to nest case expressions within a case statement (though
it
is not demonstrated here), but nesting of case statements within a
case
expression is not possible since statements do not return any value.
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set serveroutput on
declare
anum1 number := &anum1;
anum2 number := &anum2;
answer number;
begin
case anum1
when 1 then case anum2
when 1 then answer := 10;
when 2 then answer := 20;
when 3 then answer := 30;
else answer := 999;
end case;
when 2 then case anum2
when 1 then answer := 15;
when 2 then answer := 25;
when 3 then answer := 35;
else answer := 777;
end case;
else answer := 555;
end case;
dbms_output.put_line('The answer is ' || answer);
end;
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Sample 6:
This sample demonstrates nesting of case expressions within another
case
expression. Note again the absence of semicolons to terminate both
the
nested case expression and the individual cases of those
expressions.
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set serveroutput on
declare
anum1 number := &anum1;
anum2 number := &anum2;
answer number;
begin
answer :=
case anum1
when 1 then case anum2
when 1 then 10
when 2 then 20
when 3 then 30
else 999
end
when 2 then case anum2
when 1 then 15
when 2 then 25
when 3 then 35
else 777
end
else 555
end;
dbms_output.put_line('The answer is ' || answer);
end;
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Although PL/SQL anonymous blocks have been used in all of the examples
so far,
case statements and expressions can also be used in procedures,
functions, and
packages with no changes to the syntax.
The following samples are included for completeness and demonstrate the
use of
case statements and/or expressions in each of these scenarios.
Sample 7:
This sample demonstrates use of a case statement in a stored
procedure.
Note that this sample also demonstrates that it is possible for each
of
the items in the case body to consist of more than one statement.
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set serveroutput on
create or replace procedure testcasestmt ( anum IN number ) is
begin
case
when anum = 1 then dbms_output.put_line('The number was One');
dbms_output.put_line('In case 1');
when anum = 2 then dbms_output.put_line('The number was Two');
dbms_output.put_line('In case 2');
when anum = 3 then dbms_output.put_line('The number was Three');
dbms_output.put_line('In case 3');
when anum = 4 then dbms_output.put_line('The number was Four');
dbms_output.put_line('In case 4');
when anum = 5 then dbms_output.put_line('The number was Five');
dbms_output.put_line('In case 5');
else dbms_output.put_line('The description was Invalid input');
dbms_output.put_line('In the else case');
end case;
end;
exec testcasestmt(&anum);
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Sample 8:
This sample demonstrates the use of a case statement in a stored
package.
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set serveroutput on
create or replace package testpkg2 is
procedure testcasestmt ( anum IN number );
function testcasestmt_f ( anum IN number ) return number;
end testpkg2;
create or replace package body testpkg2 is
procedure testcasestmt ( anum IN number ) is
begin
case
when anum = 1 then dbms_output.put_line('The number was One');
dbms_output.put_line('In case 1');
when anum = 2 then dbms_output.put_line('The number was Two');
dbms_output.put_line('In case 2');
when anum = 3 then dbms_output.put_line('The number was Three');
dbms_output.put_line('In case 3');
when anum = 4 then dbms_output.put_line('The number was Four');
dbms_output.put_line('In case 4');
when anum = 5 then dbms_output.put_line('The number was Five');
dbms_output.put_line('In case 5');
else dbms_output.put_line('The description was Invalid input');
dbms_output.put_line('In the else case');
end case;
end;
function testcasestmt_f ( anum IN number ) return number is
begin
case
when anum = 1 then dbms_output.put_line('The number was One');
dbms_output.put_line('In case 1');
when anum = 2 then dbms_output.put_line('The number was Two');
dbms_output.put_line('In case 2');
when anum = 3 then dbms_output.put_line('The number was Three');
dbms_output.put_line('In case 3');
when anum = 4 then dbms_output.put_line('The number was Four');
dbms_output.put_line('In case 4');
when anum = 5 then dbms_output.put_line('The number was Five');
dbms_output.put_line('In case 5');
else dbms_output.put_line('The description was Invalid input');
dbms_output.put_line('In the else case');
end case;
return anum;
end;
end testpkg2;
exec testpkg2.testcasestmt(&anum);
variable numout number
exec :numout := testpkg2.testcasestmt_f(&anum);
print numout
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Sample 9:
This sample demonstrates the use of a case expression in a stored
package.
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set serveroutput on
create or replace package testpkg is
procedure testcase ( anum IN number );
function testcase_f ( anum IN number ) return number;
end testpkg;
create or replace package body testpkg is
procedure testcase ( anum IN number ) is
anumber number := anum;
anothernum number;
begin
anothernum :=
case
when anumber = 1 then anumber + 1
when anumber = 2 then anumber + 2
when anumber = 3 then anumber + 3
when anumber = 4 then anumber + 4
when anumber = 5 then anumber + 5
else 999
end;
dbms_output.put_line('The number was ' || anothernum);
end;
function testcase_f ( anum IN number ) return number is
anumber number := anum;
anothernum number;
begin
anothernum :=
case
when anumber = 1 then anumber + 1
when anumber = 2 then anumber + 2
when anumber = 3 then anumber + 3
when anumber = 4 then anumber + 4
when anumber = 5 then anumber + 5
else 999
end;
dbms_output.put_line('The number was ' || anothernum);
return anothernum;
end;
end testpkg;
variable numout number
exec testpkg.testcase(&anum);
exec :numout := testpkg.testcase_f(&anum);
print numout
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제약 사항
다음의 databasetype은 case 문에서 지원되지 않는다.
BLOB
BFILE
VARRAY
Nested Table
PL/SQL Record
PL/SQL Version 2 tables (index by tables)
Object type (user-defined type)
All of these types except for object types face a similar restriction
even for if statements (i.e. they cannot be compared for equality directly) so this is unlikely to change for these types. Lack of support for object types is simply an implementation restriction which may be relaxed in future releases.
Reference Ducumment
Oracle 8.1.7 Manual
NOTE:131557.1

Answer 1

I have done the following code but doesn't
like the statement of - "case(butNext)". What do you mean "doesn't like" -- did you get an error message?
I'm guessing it won't compile because you're trying to switch on a Button.
I tried something
like "g.fillOval(100,50,70,90, BorderLayout.NORTH)"...no that doesn't make sense. You only use BorderLayout.NORTH when you're adding components to a BorderLayout layout manager. An oval is not a component and fillOval isn't adding a component and Graphics is not a Panel or layout manager.
Would appreciate it if someone could tell me how to position
shapes using the graohic method. I think the problem is that you're confusing shapes with components.