MySQL – 如何选择’DISTINCT’重叠时段(日期或数字范围)

简洁地说,如果查询告诉我A重叠B,那么我也不需要它也告诉我B也重叠A,因为它们相互重叠.

所以我试图在sql中使用自联接来选择’DISTINCT’重叠.

为了说明,这里是一个简单的SQL小提琴,我写的是为了显示包含重叠选择(http://sqlfiddle.com/#!9/7af84f/1)

详细地…

假设我有一个名称(char),d1(int),d2(int)的表,其架构如下.这里d1和d2表示某个间隔的开始和结束,该间隔可能与同一个表中的另一个间隔重叠.

CREATE TABLE test (
  letter char ,
  d1 int ,
  d2 int  
) ;

鉴于此表,我填写了一些值

INSERT INTO test (letter,d1,d2)
VALUES
   ('A',  2, 10),    -- overlaps C and D
   ('B', 12, 20),    -- overlaps E
   ('C',  5, 10),    -- overlaps A and D
   ('D',  1,  8),    -- overlaps A and C 
   ('E', 13, 15),    -- overlaps B
   ('F', 25, 30);    -- doesn't overlap anything

并运行以下查询,该查询使用自联接来正确查找其中一行中的d1和d2与其他行中的d1和d2包含重叠的行.

-- selects all records that overlap in the range d1 - d2 inclusive
-- (excluding the implicit overlap between a record and itself)
-- The results are sorted by letter followed by d1

SELECT
  basetable.letter as test_letter,
  basetable.d1,
  basetable.d2,
  overlaptable.letter as overlap_letter,
  overlaptable.d1 as overlap_d1,
  overlaptable.d2 as overlap_d2

FROM
  test as basetable, 
  test as overlaptable
WHERE
  -- there is an inclusive overlap
  basetable.d1 <= overlaptable.d2 and basetable.d2 >= overlaptable.d1
AND
  -- the row being checked is not itsself
    basetable.letter <> overlaptable.letter
    AND
    basetable.d1 <> overlaptable.d1
    AND 
    basetable.d2 <> overlaptable.d2
ORDER BY 
  basetable.letter,
  basetable.d1

这正确地给了我以下,显示了所有6个版本的重叠,例如左手栏表示A重叠C而另一行显示C重叠A(注意sqlfiddle似乎不理解字段别名所以我的列标题不同)

test_letter     d1     d2   overlap_letter  overlap_d1  overlap_d2
  A              2     10         D              1         8
  B             12     20         E             13        15
  C              5     10         D              1         8
  D              1      8         A              2        10
  D              1      8         C              5        10
  E             13     15         B             12        20

我的问题是：

如何更改sql以获得四行’DISTINCT’或’单向’重叠？

即这个结果……

test_letter  d1     d2  overlap_letter  overlap_d1  overlap_d2 
    A         2     10        D            1           8
    A         2     10        C            5          10
    B        12     20        E           13          15
    C         5     10        D            1           8

例如：
 根据以下推理,只显示左侧列中A,B和C的记录的结果

> A(2,10)与D(1,8)和C(5,10)重叠,{显示这两行}
> B(12,20)与E重叠(13,15){显示此行}
> C(5,10)与D(1,8)重叠{显示此行但不显示A(1,10)重叠,因为第2行已显示A和C重叠}
> D(1,8){不要显示我们已经知道的关于A(1,10)和C(5,10)的任何新内容
> E(13,15){不要显示我们已经知道的关于B(12,20)的任何新内容
> F(25,30){由于没有重叠,所以不要显示任何内容}

解决方法:

你可以改变不平等.而且,你还应该使用JOIN：

SELECT basetable.letter as test_letter, basetable.d1, basetable.d2,
       overlaptable.letter as overlap_letter, overlaptable.d1 as overlap_d1, overlaptable.d2 as overlap_d2
FROM test basetable JOIN
     test overlaptable
     ON basetable.d1 <= overlaptable.d2 AND
        basetable.d2 >= overlaptable.d1
WHERE basetable.letter < overlaptable.letter  -- This is the change
ORDER BY basetable.letter, basetable.d1;

标签：mysql,sql,distinct,overlapping
来源： https://codeday.me/bug/20190702/1352530.html