您可以通过多种方式进行这种分解，但与单个 SQL 语句相比，所有这些方式都会显着降低性能。
可维护性改进也值得商榷，取决于具体情况。
要查看所有可能性，请查看documentation。
以下是一些基于简单逻辑的可能变体：
- 根据给定的Id计算Oracle用户名前缀；
- 获取名称以该前缀开头的所有用户；
- 从步骤 2 中查找用户拥有的所有表；
- 统计找到的表的总数。
1.流水线
准备函数使用的类型：
create or replace type TUserRow as object (
username varchar2(30),
user_id number,
created date
)
/
create or replace type TTableRow as object (
owner varchar2(30),
table_name varchar2(30),
status varchar2(8),
logging varchar2(3)
-- some other useful fields here
)
/
create or replace type TUserList as table of TUserRow
/
create or replace type TTableList as table of TTableRow
/
通过用户ID查找前缀的简单函数：
create or replace function GetUserPrefix(piUserId in number) return varchar2
is
vUserPrefix varchar2(30);
begin
select substr(username,1,3) into vUserPrefix
from all_users
where user_id = piUserId;
return vUserPrefix;
end;
/
用户搜索功能：
create or replace function GetUsersPipe(
piNameStart in varchar2
)
return TUserList pipelined
as
vUserList TUserList;
begin
for cUsers in (
select *
from
all_users
where
username like piNameStart||'%'
)
loop
pipe row( TUserRow(cUsers.username, cUsers.user_id, cUsers.created) ) ;
end loop;
return;
end;
表格搜索功能：
create or replace function GetUserTablesPipe(
piUserNameStart in varchar2
)
return TTableList pipelined
as
vTableList TTableList;
begin
for cTables in (
select *
from
all_tables tab_list,
table(GetUsersPipe(piUserNameStart)) user_list
where
tab_list.owner = user_list.username
)
loop
pipe row ( TTableRow(cTables.owner, cTables.table_name, cTables.status, cTables.logging) );
end loop;
return;
end;
代码中的用法：
declare
vUserId number := 5;
vTableCount number;
begin
select count(1) into vTableCount
from table(GetUserTablesPipe(GetUserPrefix(vUserId)));
dbms_output.put_line('Users with name started with "'||GetUserPrefix(vUserId)||'" owns '||vTableCount||' tables');
end;
2。简单的表格函数
此解决方案使用与具有上述流水线功能的变体相同的类型。
用户搜索功能：
create or replace function GetUsers(piNameStart in varchar2) return TUserList
as
vUserList TUserList;
begin
select TUserRow(username, user_id, created)
bulk collect into vUserList
from
all_users
where
username like piNameStart||'%'
;
return vUserList;
end;
/
表格搜索功能：
create or replace function GetUserTables(piUserNameStart in varchar2) return TTableList
as
vTableList TTableList;
begin
select TTableRow(owner, table_name, status, logging)
bulk collect into vTableList
from
all_tables tab_list,
table(GetUsers(piUserNameStart)) user_list
where
tab_list.owner = user_list.username
;
return vTableList;
end;
/
代码中的用法：
declare
vUserId number := 5;
vTableCount number;
begin
select count(1) into vTableCount
from table(GetUserTables(GetUserPrefix(vUserId)));
dbms_output.put_line('Users with name started with "'||GetUserPrefix(vUserId)||'" owns '||vTableCount||' tables');
end;
3.光标 - xml - 光标
这是一种特殊情况，可以在没有用户定义类型的情况下实现，但性能损失很大，涉及不需要的类型转换，可维护性低。
用户搜索功能：
create or replace function GetUsersRef(
piNameStart in varchar2
)
return sys_refcursor
as
cUserList sys_refcursor;
begin
open cUserList for
select * from all_users
where username like piNameStart||'%'
;
return cUserList;
end;
表格搜索功能：
create or replace function GetUserTablesRef(
piUserNameStart in varchar2
)
return sys_refcursor
as
cTableList sys_refcursor;
begin
open cTableList for
select
tab_list.*
from
(
XMLTable('/ROWSET/ROW'
passing xmltype(GetUsersRef(piUserNameStart))
columns
username varchar2(30) path '/ROW/USERNAME'
)
) user_list,
all_tables tab_list
where
tab_list.owner = user_list.username
;
return cTableList;
end;
代码中的用法：
declare
vUserId number := 5;
vTableCount number;
begin
select count(1) into vTableCount
from
XMLTable('/ROWSET/ROW'
passing xmltype(GetUserTablesRef(GetUserPrefix(vUserId)))
columns
table_name varchar2(30) path '/ROW/TABLE_NAME'
)
;
dbms_output.put_line('Users with name started with "'||GetUserPrefix(vUserId)||'" owns '||vTableCount||' tables');
end;
当然，所有变体都可以混合使用，但 SQL 至少在简单情况下看起来更好：
declare
vUserId number := 5;
vUserPrefix varchar2(100);
vTableCount number;
begin
-- Construct prefix from Id
select max(substr(user_list.username,1,3))
into vUserPrefix
from
all_users user_list
where
user_list.user_id = vUserId
;
-- Count number of tables owned by users with name started with vUserPrefix string
select
count(1) into vTableCount
from
all_users user_list,
all_tables table_list
where
user_list.username like vUserPrefix||'%'
and
table_list.owner = user_list.username
;
dbms_output.put_line('Users with name started with "'||vUserPrefix||'" owns '||vTableCount||' tables');
end;
附注所有代码仅用于演示目的：没有优化等等。