PL/SQL的三种形式的循环：
1.LOOP（无条件循环）：
loop
statements;
end loop;
2.WHILE（有条件循环）：
while condition loop
statements;
end loop;
3.FOR（固定次数循环）：
for counter in value1 .. value2
loop
statements;
end loop;
实例：分别用三种循环输出1-100
loop:
declare i number;
begin i := 1; loop if i > 100
then goto quit;
end if; dbms_output.put_line(i); i := i + 1;
end loop; <<quit>>
null;
end;
declare i number;
begin
i := 1;
loop
if i > 100 then
goto quit;
end if;
dbms_output.put_line(i);
i := i + 1;
end loop;
<<quit>>
null;
end;
while:
declare i number;
begin i := 1; while i<=100 loop dbms_output.put_line(i); i := i+1;
end loop;
end;
declare
i number;
begin
i := 1;
while i<=100 loop
dbms_output.put_line(i);
i := i+1;
end loop;
end;
for:
declare i number;
begin for i
in 1..100 loop dbms_output.put_line(i);
end loop;
end;
