循环原则：
如果循环内部必须执行一次，则使用基本循环
如果知道循环次数，则使用FOR循环
如果必须在每次循环开始时判断条件，则使用WHILE循环
1、基本循环
SQL> declare
2 i number := 0;
3 begin
4 loop
5 dbms_output.put_line(i);
6 i := i+1;
7 exit when i = 10;
8 end loop;
9 end;
10 /
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PL/SQL procedure successfully completed.
SQL> declare
2 i number := 0;
3 begin
4 loop
5 i := i+1;
6 dbms_output.put_line(i);
7 exit when i = 10;
8 end loop;
9 end;
10 /
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10
PL/SQL procedure successfully completed.
2、FOR循环
SQL> declare
2 i number := 0 ;
3 begin
4 for i in 0 .. 10 loop
5 dbms_output.put_line(i);
6 end loop;
7 end;
8 /
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10
PL/SQL procedure successfully completed.
3、WHILE循环
SQL> declare
2 i number:=0;
3 begin
4 while i<=10 loop
5 dbms_output.put_line(i);
6 i:=i+1;
7 end loop;
8 end;
9 /
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PL/SQL procedure successfully completed.