测试 Oracle 中对 char 和 varchar2 两种类型的等值比较

 
我们用 Oracle 的 SQL*Plus 执行 SQL 语句。首先看看 Oracle 的版本号：

SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.1.0.2.0 - Prod
PL/SQL Release 10.1.0.2.0 - Production
CORE 10.1.0.2.0 Production
TNS for 32-bit Windows: Version 10.1.0.2.0 - Production
NLSRTL Version 10.1.0.2.0 - Production

其次打开服务器端的输出信息：

set serveroutput on;
--
-- column type is char, but parameter type is varchar.
--
drop table foo;
create table foo(fno number(4), fname char(20));
insert into foo values(1, 'smith');
insert into foo values(2, 'john');

SQL> select * from foo where fname = 'smith';

FNO FNAME
---------- --------------------
1 smith

SQL> select * from foo where fname = cast('smith' as char(20));

FNO FNAME
---------- --------------------
1 smith

注意，varchar2 找不出结果：

SQL> select * from foo where fname = cast('smith' as varchar2(20));

no rows selected
现在，我们换成存储过程试试。

create or replace procedure foop(bname varchar2)
as
    v_fno number(4);
    v_fname char(20);
begin
    dbms_output.put_line('in procedure');
    select fno, fname into v_fno, v_fname from foo where fname = bname;
    dbms_output.put_line('results: ' || v_fno || ',' || v_fname );

exception
    when no_data_found then
    dbms_output.put_line('employee ' || bname || ' not found');
when others then
    dbms_output.put_line('the following is sqlerrm:');
    dbms_output.put_line(sqlerrm);
    dbms_output.put_line('the following is sqlcode:');
    dbms_output.put_line(sqlcode);
end;
/

call foop('smith');

用 varchar2 做存储过程的参数也是找不出结果。

Expected result:
<result>
in procedure
employee smith not found

Call completed.
</result>
create or replace procedure foop2(bname char)
as
    v_fno number(4);
    v_fname char(20);
begin
    dbms_output.put_line('in procedure');
    select fno, fname into v_fno, v_fname from foo where fname = bname;
    dbms_output.put_line('results: ' || v_fno || ',' || v_fname );
exception
    when no_data_found then
    dbms_output.put_line('employee ' || bname || ' not found');
when others then
    dbms_output.put_line('the following is sqlerrm:');
    dbms_output.put_line(sqlerrm);
    dbms_output.put_line('the following is sqlcode:');
    dbms_output.put_line(sqlcode);
end;
/

call foop2('smith');

用 char 作为存储过程的参数，还是能够找出结果的。

Expected results:
<result>
in procedure
results: 1,smith

Call completed.
</result>
下面我们测试一下列的类型是 varchar2 的情况。

--
-- column type is varchar, but parameter type is char.
--
drop table foo;
create table foo(fno number(4), fname varchar2(20));
insert into foo values(1, 'smith');
insert into foo values(2, 'john');

SQL> select * from foo where fname = 'smith';

FNO FNAME
---------- --------------------
1 smith

SQL> select * from foo where fname = cast('smith' as varchar2(20));

FNO FNAME
---------- --------------------
1 smith

注意，用 char 是找不出结果的：

SQL> select * from foo where fname = cast('smith' as char(20));

no rows selected

create or replace procedure foop(bname char)
as
v_fno number(4);
v_fname varchar2(20);
begin
dbms_output.put_line('in procedure');
select fno, fname into v_fno, v_fname from foo where fname = bname;
dbms_output.put_line('results: ' || v_fno || ',' || v_fname );

exception
when no_data_found then
dbms_output.put_line('employee ' || bname || ' not found');
when others then
dbms_output.put_line('the following is sqlerrm:');
dbms_output.put_line(sqlerrm);
dbms_output.put_line('the following is sqlcode:');
dbms_output.put_line(sqlcode);
end;
/

call foop('smith');

存储过程的参数为 char 时，居然也可以找出该记录。

Expected result:
<result>
in procedure
results: 1,smith

Call completed.
</result>
create or replace procedure foop2(bname varchar2)
as
    v_fno number(4);
    v_fname varchar2(20);
begin
    dbms_output.put_line('in procedure');
    select fno, fname into v_fno, v_fname from foo where fname = bname;
    dbms_output.put_line('results: ' || v_fno || ',' || v_fname );
exception
when no_data_found then
    dbms_output.put_line('employee ' || bname || ' not found');
    when others then
    dbms_output.put_line('the following is sqlerrm:');
    dbms_output.put_line(sqlerrm);
    dbms_output.put_line('the following is sqlcode:');
    dbms_output.put_line(sqlcode);
end;
/

call foop2('smith');

存储过程参数为 varchar2 时当然更应该能找出该记录了。

Expected results:
<result>
in procedure
results: 1,smith

Call completed.
</result>
1. http://www.psoug.org/reference/dbms_output.html