生成记录的分散数量

Question

我有一些代码正在生成父级，并为每个父级生成随机数量的子级记录。我希望每个父母有5条或更多的子记录，并且少于20条。

我跑了几次，但似乎没有得到或很少有5-13范围内的子记录。

有人可以解释一下我如何获得更分散的子记录价值。

如果您运行下面的最后一个查询，您将看到没有计数（*）或值6-15中的计数很少。

毫无疑问，我的逻辑有问题，但似乎找不到。我也欢迎任何完成相同任务并使用INSERT all语句生成大量子记录的新代码。

我的目标是生成大量测试数据以检查应用程序查询。目前，我只产生30天的价值。

   CREATE TABLE emp_info
    (
      empid INTEGER,
     empname VARCHAR2(50)
   );


CREATE TABLE  emp_attendance    
(empid INTEGER,
 start_date DATE,
 end_date DATE
 );


insert all 
  -- when rn=1 insert the parent record.
  -- 1 will always =1 always insert a
  -- child record.
when rn = 1 then into emp_info   (empid, empname) values (id, name)
  when  1 = 1 then into emp_attendance (empid, start_date, end_date) 

   values (id, d1, d1 + dbms_random.value (0, .75))
select * from 
(

-- get the highest empid as start
-- so this can be run more than once.
-- if never run before start with 0.

with t as (select nvl(max(empid), 0)     maxid from emp_info)
select ceil(maxid + level/20) id,
   case mod(maxid + level, 20) when 1 then 1 end rn, 

  -- create an alpha name from 3-15
  -- characters in length.


 dbms_random.string('U',     dbms_random.value(3, 15)) name, 

-- set the start date any where from
-- today + 30 days

trunc(sysdate) +    dbms_random.value (1, 30) d1,      

case when row_number() over (partition by ceil(maxid + level/20)                            order by level) > 5 then

 -- Ensure there is a minimum of
 -- 5 child and a max of 20 records 
   -- for each parent.
    --
   -- Exclude first 5 records and then  
   -- for 6-20 records, generating 
  -- random number between 5-20. 
  -- We can then compare with any 
    -- number between 5-20 so that it 
   -- can give us any number of 
   -- records.

 dbms_random.value(5, 20)        else 5 end as random_val  from t   

    connect by level <= 20 * 1000
)  
where random_val <= 19;
 -- why is this where clause neeed?

SELECT empid, count(*) 
from  emp_attendance
 group by empid order by empid 


EMPID    COUNT(*)
1    20
2    20
3    20
4    18
5    19
6    20
7    20
8    19
9    20
10    20   
11    19
……
 50.         20     

Answer 1

这样的事情应该可以帮助您。

SQL> with
  2    emps as
  3      ( select level empid, dbms_random.value(5,20) children from dual connect by level <= 20 ),
  4    empatt as
  5      ( select e.empid , x.start_date, x.start_date+dbms_random.value(0,0.75) end_date
  6        from emps e,
  7             lateral(
  8               select
  9                 trunc(sysdate)+dbms_random.value(1,30) start_date
 10               from dual
 11               connect by level <= e.children
 12               ) x
 13       )
 14  select empid, count(*)
 15  from empatt
 16  group by empid
 17  order by 1;

     EMPID   COUNT(*)
---------- ----------
         1          5
         2         14
         3         17
         4          6
         5         10
         6         18
         7         12
         8         13
         9         16
        10         11
        11          7
        12         14
        13          7
        14          7
        15          7
        16         13
        17         18
        18          9
        19          9
        20         12