Oracle PL/SQL:IF語句的基本使用

原文:http://psoug.org/reference/control_struct.html
IF語句的使用
A.基本的IF條件語句：
基本語法:

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IF THEN
  
END IF;


Example:

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SQL> set serveroutput on;
SQL> declare
   x number(3):=9;
    begin
    if x<10 then
    dbms_output.put_line('x is less than10');
    end if;
   end;
   /

結果：
x is less than10

PL/SQL procedure successfully completed



B.IF - ELSE 語句

基本語法：

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IF THEN
  
ELSE
  
END IF;


Example:

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DECLARE
x NUMBER(3) := 10;
BEGIN
  IF x < 10 THEN
    dbms_output.put_line('X is less than 10');
  ELSE
    dbms_output.put_line('X is not less than 10');
  END IF;
END;
/

結果：
X is not less than 10

PL/SQL procedure successfully completed


C:IF - ELSIF - ELSE 語句

基本語法:

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IF THEN
  
ELSIF THEN
  
ELSIF THEN
  
ELSE
  
END IF;



Example:

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set serveroutput on

DECLARE
x NUMBER(3) := 47;
BEGIN
  IF x < 10 THEN
    dbms_output.put_line('X is less than 10');
  ELSIF x = 10 THEN
    dbms_output.put_line('X is equal to 10');
  ELSIF x < 100 THEN
    dbms_output.put_line('X is between 11 and 99');
  ELSE
    dbms_output.put_line('X is greater than 99');
  END IF;
END;
/

結果：
X is between 11 and 99

PL/SQL procedure successfully completed


D:與NULL值比較處理

Example:

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declare
       v NUMBER;
   begin
       if v = 1 then
           DBMS_OUTPUT.put_line('Equal to 1');
       elsif v!= 1 then
           DBMS_OUTPUT.put_line('Not equal to 1');
       elsif v = v then
           DBMS_OUTPUT.put_line('Equal to itself');
       else
           DBMS_OUTPUT.put_line('Undefined result');
       end if;
       v:=v+1;
       DBMS_OUTPUT.put_line('New value: <'||v||'>');
   end;
/

結果:

Undefined result
New value: <>