Oracle扩展PL/SQL简介(二)

4. 块语句

1) 块的结构和变量声明：

DECLARE

变量说明部分；

BEGIN

执行语句部分；

[EXCEPTION

例外处理部分；]

END;

2) 控制语句：

IF语句：

IF condition THEN

Sequence_of_statements;

END IF;

IF condition THEN

Sequence_of_statement1;

ELSE

Sequence_of_statement2;

END IF;

IF condition1 THEN

Sequence_of_statement1;

ELSIF condition2 THEN

Sequence_of_statement2;

ELSIF condition3 THEN

Sequence_of_statement3;

END IF;

举例：

declare

v1 date:=to_date(' 2007-04-2', 'yyyy-mm-dd');

v2 boolean;

begin

if months_between(sysdate,v1) >5 then

v2 := true;

dbms_output.put_line('true');

else

v2:=false;

dbms_output.put_line('false');

end if;

end;

/

[<<label_name>>]

CASE selector

WHEN expression1 THEN

sequence_of_statements1;

WHEN expression2 THEN

sequence_of_statements2;

...

WHEN expressionn THEN

sequence_of_statementsn;

[ELSE sequence_of_statementsN+1;]

END [CASE [label_name];

举例：

declare

v1 char(1):=upper('&v1');

v2 varchar2(20);

begin

v2:=case v1

when 'A' then 'Excellent'

when 'B' then 'Very Good'

when 'C' then 'Good'

else 'No such grade'

end;

dbms_output.put_line(chr(10) ||'level '|| v1 ||' is '||v2);

end;

/

3) 循环语句：

基本循环

LOOP

Sequence_of_statements;

IF condition THEN

EXIT;

END IF;

END LOOP;

例子：

create table t1 (c1 number(2));

---------------------------

declare

v1 number(2):=1;

begin

loop

insert into t1 values(v1);

v1:=v1+1;

exit when v1>10;

end loop;

end;

/

WHILE循环

WHILE condition LOOP

Sequence_of_statements;

END LOOP;

举例：

declare

v1 number(2):=1;

begin

while v1<10 loop

insert into t1 values(v1);

v1:=v1+1;

end loop;

end;

/

FOR循环

FOR counter IN lower_bound..higher_bound LOOP

Sequence_of_statements;

END LOOP;

举例：

begin

dbms_output.put_line(chr(10)||' ----');

for v1 in reverse 1..9 loop

dbms_output.put_line(v1);

insert into t1 values(v1);

end loop;

dbms_output.put_line(' ----');

end;

/