意外的結果使用CTE在所有行的兩個表上執行隨機連接一對多

Question

我試圖隨機連接兩個表（TableA和TableB）的行，使TableA中的每一行都只連接到一個TableB中的每一行，並且TableB中的每一行都連接到TableA中的至少一行。

例如，隨機加入與5個不同的行和表B具有3個不同的行表A的應導致這樣的事情：

TableA TableB 
1  3 
2  1 
3  1 
4  2 
5  1 

然而，有時不是所有的從表B中的行包括在最終結果;因此在上面的示例中可能會丟失TableB中的第2行，因爲它的位置是第1行或第3行連接到TableA上的第4行。您可以通過多次執行腳本並檢查結果來看到發生這種情況。似乎有必要使用臨時表（@Q）來確保返回包含TableA和TableB中所有行的正確結果。

有人可以解釋爲什麼會發生這種情況嗎？

另外，有人可以請建議什麼會是一個更好的方式來獲得所需的結果？

據我所知，有時沒有結果返回，因爲交叉應用中的某種失敗以及我尚未確定的順序，並且我確信有更好的方法來執行此操作。我希望這是有道理的。提前致謝！

declare @TableA table (
     ID int 
     ); 
    declare @TableB table (
     ID int 
     ); 
    declare @Q table (
     RN int, 
     TableAID int, 
     TableBID int 
     ); 

    with cte as (
     select 
      1 as ID 
     union all 
     select 
      ID + 1 
     from cte 
     where ID < 5 
     ) 
    insert @TableA (ID) 
    select ID from cte; 

    with cte as (
     select 
      1 as ID 
     union all 
     select 
      ID + 1 
     from cte 
     where ID < 3 
     ) 
    insert @TableB (ID) 
    select ID from cte; 

    select * from @TableA; 
    select * from @TableB; 

    with cte as (
     select 
      row_number() over (partition by TableAID order by newid()) as RN, 
      TableAID, 
      TableBID 
     from (
      select 
       a.ID as TableAID, 
       b.ID as TableBID 
      from @TableA as a 
      cross apply @TableB as b 
      ) as M 
     ) 
    select --All rows from TableB not always included 
     TableAID, 
     TableBID 
    from cte 
    where RN in (
     select 
      top 1 
       iCTE.RN 
     from cte as iCTE 
     group by iCTE.RN 
     having count(distinct iCTE.TableBID) = (
      select count(1) from @TableB 
      ) 
     ) 
    order by TableAID; 

    with cte as (
     select 
      row_number() over (partition by TableAID order by newid()) as RN, 
      TableAID, 
      TableBID 
     from (
      select 
       a.ID as TableAID, 
       b.ID as TableBID 
      from @TableA as a 
      cross apply @TableB as b 
      ) as M 
     ) 
    insert @Q 
    select 
     RN, 
     TableAID, 
     TableBID 
    from cte; 

    select * from @Q; 

    select --All rows from both TableA and TableB included 
     TableAID, 
     TableBID 
    from @Q 
    where RN in (
     select 
      top 1 
       iQ.RN 
     from @Q as iQ 
     group by iQ.RN 
     having count(distinct iQ.TableBID) = (
      select count(1) from @TableB 
      ) 
     ) 
    order by TableAID; 

Answer 1

看看這給了你，你找什麼？

DECLARE 
    @CountA INT = (SELECT COUNT(*) FROM @TableA ta), 
    @CountB INT = (SELECT COUNT(*) FROM @TableB tb), 
    @MinCount INT; 

SELECT @MinCount = CASE WHEN @CountA < @CountB THEN @CountA ELSE @CountB END; 

WITH 
    cte_A1 AS (
     SELECT 
      *, 
      rn = ROW_NUMBER() OVER (ORDER BY NEWID()) 
     FROM 
      @TableA ta 
     ), 
    cte_B1 AS (
     SELECT 
      *, 
      rn = ROW_NUMBER() OVER (ORDER BY NEWID()) 
     FROM 
      @TableB tb 
     ), 
    cte_A2 AS (
     SELECT 
      a1.ID, 
      rn = CASE WHEN a1.rn > @MinCount THEN a1.rn - @MinCount ELSE a1.rn end 
     FROM 
      cte_A1 a1 
     ), 
    cte_B2 AS (
     SELECT 
      b1.ID, 
      rn = CASE WHEN b1.rn > @MinCount THEN b1.rn - @MinCount ELSE b1.rn end 
     FROM 
      cte_B1 b1 
     ) 
SELECT 
    A = a.ID, 
    B = b.ID 
FROM 
    cte_A2 a 
    JOIN cte_B2 b 
     ON a.rn = b.rn;