Question

基本上，我有以下查询（实际上更复杂，但我认为这种简化是可以的）：

SELECT a, b, x
FROM table

output:

 a | b | x
-----------
 1 | 2 | 34
 1 | 3 | 35
 1 | 3 | 36
 1 | 4 | 37
 2 | 3 | 38
 2 | 3 | 39
 2 | 4 | 40
 3 | 4 | 41
 3 | 5 | 42

要计算每个＆＃34;对a和b＆＃34;的发生次数，我使用GROUP BY：

SELECT a, b, COUNT(x) AS count
FROM table
GROUP BY a, b
ORDER BY count

output:

 a | b | count
--------------
 1 | 2 | 1
 1 | 4 | 1
 2 | 4 | 1
 3 | 4 | 1
 3 | 5 | 1
 1 | 3 | 2
 2 | 3 | 2

困扰我的是a和b的多重出现。我想保持＆＃34;计数＆＃34;如果a或b已经在前一行中，则删除每一行。如果它还会移除一行，如果＆＃34; a＆＃34;的值，那将是一件好事。出现在前一行中作为＆＃34; b＆＃34;反之亦然。

首选预期输出：

 a | b | count
--------------
 1 | 2 | 1
 1 | 4 | 1    <- should not be in output since we had a=1
 2 | 4 | 1    <- should not be in output since we had b=
 3 | 4 | 1    
 3 | 5 | 1    <- should not be in output since we had a=3
 1 | 3 | 2    <- should not be in output since we had a=1 / a=3
 2 | 3 | 2    <- should not be in output since we had b=2 / a=3

因此，这个：

 a | b | count
--------------
 1 | 2 | 1
 3 | 4 | 1

替代预期输出，如果上述情况过于复杂：

 a | b | count
--------------
 1 | 2 | 1
 1 | 4 | 1    <- should not be in output since we had a=1
 2 | 4 | 1    
 3 | 4 | 1    <- should not be in output since we had b=4
 3 | 5 | 1    
 1 | 3 | 2    <- should not be in output since we had a=1
 2 | 3 | 2    <- should not be in output since we had a=2

因此，这个：

 a | b | count
--------------
 1 | 2 | 1
 2 | 4 | 1    
 3 | 5 | 1

Answer 1

这是一个混乱的问题，但这里需要考虑的事情：

SELECT a, b, count
FROM (
    SELECT a, b, count,
          rank() over (partition by b order by count, a) as b_rank
    FROM (
        SELECT a, b, count,
          rank() over (partition by a order by count, b) as a_rank
        FROM (
            SELECT a, b, COUNT(*) AS count
            FROM t
            GROUP BY a, b
            ORDER BY count
          ) pc
      ) pc2
    WHERE a_rank < 3
  ) pc3
WHERE b_rank = 1

每个a值在结果中最多显示两次，但b值将是唯一的。出现在低计数对中的某些b值可能不会反映在结果中。可能会重复a与可能完全错过的b值的数量之间存在权衡：允许更多重复a（通过更改为WHERE a_rank < 4 }}）减少可能遗漏的b值的数量。

Answer 2

此查询将为您提供所需的输出。

DECLARE @id INT = 1,
        @a INT,
        @b INT,
        @count INT

DECLARE @tbl TABLE
(
    id INT IDENTITY(1,1),
    a INT,
    b INT,
    count INT
)

INSERT INTO @tbl
SELECT a, b, COUNT(1) AS COUNT FROM dbo.myTable
GROUP BY a, b
ORDER BY COUNT,a,b

SELECT @count = COUNT(1) FROM @tbl

WHILE @id <= @count
BEGIN
    SELECT TOP 1 @a = a,@b = b FROM @tbl WHERE id = @id

    IF EXISTS(SELECT 1 FROM @tbl WHERE id < @id AND (a = @a OR b = @b))
        DELETE @tbl WHERE id = @id

    SET @id += 1
END

SELECT a,b,count FROM @tbl

Check it on SQLFiddle

已应用GROUP BY后，多列的值不同

2 个答案: