SQL Intersection和Union

Question

我有一个名为words的表格，由三列word(VARCHAR(16)), doc_id(INT), weight(DOUBLE)组成。

这是我需要做的，我有两个问题：

SELECT doc_id, weight FROM words WHERE word = 'bla';

doc_id    weight
------    ------
1         0.14
2         0.61
3         0.32

和

SELECT doc_id, weight FROM words WHERE word = 'blabla';

doc_id    weight
------    ------
2         0.19
3         0.45
4         0.14

我需要在doc_id上获取两者的交集，并选择较低的weight值作为权重，即我希望结果为：

doc_id    weight
------    ------
2         0.19
3         0.32

有没有办法在单个查询中执行此操作？在程序中这样做会让它变慢！

我还需要获取UNION并选择较高的weight值，即我希望结果为：

doc_id    weight
------    ------
1         0.14
2         0.61
3         0.45
4         0.14

请注意，word和doc_id列不是唯一的，因此可以将一个字分配给多个文档。

Answer 1

对于交叉部分，听起来你想要“所有doc_id的最低权重，其中doc_id对于单词'bla'有一行而对于'blabla'这个单词有一行”。

可以找到

(untested)
select w1.doc_id, least(min(w1.weight), min(w2.weight)) as minweight 
  from words w1, words w2
 where w1.doc_id = w2.doc_id
   and w1.word = 'bla'
   and w2.word = 'blabla'
 group by w1.doc_id;

对于联合部分，你想要的是“所有doc_id的最高权重，其中doc_id有一行'bla'或一行'blabla'”。

可以找到

(untested)
select doc_id, max(weight) as maxWeight
  from words
 where word in ('bla', 'blabla')
 group by doc_id;

Answer 2

select w1.doc_id
     , least(w1.weight, w2.weight) weight
  from words w1
 inner 
  join words w2
    on w1.doc_id = w2.doc_id
 where w1.word = 'bla1'
   and w2.word = 'bla2'



select doc_id
     , max(weight) weight
  from words
 where word in ('blah1', 'blah2')
 group
    by doc_id

Answer 3

我认为你想要这个：

SELECT doc_id, MIN(weight) MinWeight, MAX(weight) MaxWeight
FROM words
WHERE word IN ('bla','blabla')
GROUP BY doc_id

Answer 4

路口：

SELECT doc_id, MIN(weight) as MinWeight FROM words
WHERE doc_id IN
    (SELECT doc_id FROM words WHERE word = 'bla')
AND doc_id IN
    (SELECT doc_id FROM words WHERE word = 'blabla')
GROUP BY doc_id

联：

SELECT doc_id, MAX(weight) as MaxWeight FROM words
WHERE word IN ('bla', 'blabla')
GROUP BY doc_id

Answer 5

根据我的理解，以下查询应该适用于您的要求。

- 降低重量查询 选择Z.doc_id，MIN（权重）为LOWER_WEIGHT 从 （ SELECT doc_id，weight FROM words WHERE word ='bla' 相交 SELECT doc_id，weight FROM words WHERE word ='blabla' ）z GROUP BY Z.DOC_ID;

- 更高权重查询

选择Z.doc_id，MAX（权重）为HIGHER_WEIGHT 从 （ SELECT doc_id，weight FROM words WHERE word ='bla' 联盟 SELECT doc_id，weight FROM words WHERE word ='blabla' ）z GROUP BY Z.DOC_ID;

此致 Venk