zab08 <zab08@126.com> wrote:
>
> I have two table:
>
>
> CREATE TABLE roles(role_name varchar(255) primary key);
>
> CREATE TABLE roles_permissions(permission varchar(100), role_name varchar
> (100));
>
> here is result by :
> SELECT * from roles;
> role_name
> -----------
> role1
> role2
> (2 rows)
>
> here is result by :
> SELECT * from roles_permissions ;
> role_name | permission
> -----------+-------------
> role1 | permission1
> role1 | permission2
> role2 | permission1
> (3 rows)
>
> ---------------------------------------- -----------------------------------
>
> after the command:
> SELECT * from roles, roles_permissions;
That's a CROSS-JOIN
> role_name | role_name | permission
> -----------+-----------+-------------
> role1 | role1 | permission1
> role1 | role1 | permission2
> role1 | role2 | permission1
> role2 | role1 | permission1
> role2 | role1 | permission2
> role2 | role2 | permission1
>
>
> the expected result is:
> role_name | permission
> -----------+-------------
> role1 | permission1,permission2,
> & nbsp;role2 | permission1
>
>
> for short:
> afer join of two table, here is some repeat columns,
yeah, it's a cross-join. Rewrite your query, adding a WHERE-condition:
where roles.role_name = roles_permissions.role_name
Regards, Andreas
--
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unintentional side effect. (Linus Torvalds)
"If I was god, I would recompile penguin with --enable-fly." (unknown)
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