有没有办法在这种类型的SQL SELECT中删除嵌套查询? [英] Is there a way to remove the nested query in this type of SQL SELECT?

问题描述

鉴于此表结构和示例数据(查询中不应使用t3，仅在此处显示t1与t2之间的关系):

Given this table structure and example data (t3 should not be used in the query, it is only here to show the relation between t1 and t2):

      t1                 t2                         t3
--------------   -----------------   --------------------------------
| id | value |   | t1key | t3key |   | id | value                   |
|  1 |  2008 |   |     3 |     1 |   |  1 | "New intel cpu in 2010" |
|  2 |  2009 |   |     4 |     1 |   |  2 | "New amd cpu in 2008"   |
|  3 |  2010 |   |     6 |     1 |   |    |                     ... |
|  4 | intel |   |     1 |     2 |   --------------------------------
|  5 |   amd |   |     5 |     2 |
|  6 |   cpu |   |     6 |     2 |
|    |   ... |   |       |   ... |
--------------   -----------------

如何构建满足以下条件的SQL查询:

How would you build a SQL query that would satisfy the following:

Given the input for t1.id is the set {6} returns t1.id set {3,4,6,1,5}
Given the input for t1.id is the set {6,4} returns t1.id set {3,4,6}
Given the input for t1.id is the set {5,4} returns t1.id set {}

并且当表更大时不会影响性能吗?

and doesn't kill performance when the tables are bigger...?

推荐答案

不清楚您想要什么.

我将调用表t1 word，调用表t3 phrase和调用表t2 word is in phrase.

I will call table t1 word, call table t3 phrase and call table t2 word is in phrase.

然后我想您想找到与特定的word.id组在同一短语中的所有word.id.正确吗?

Then I guess you want to find all word.ids that are in a same phrase as a specific set of word.ids. Is that correct?

SELECT DISTINCT t1.id
FROM t1 
  JOIN t2
    ON t1.id = t2.t1key
  JOIN t2 copyt2
    ON copyt2.t3key = t2.t3key 
WHERE copyt2.t1key IN
  (6,4)       --what you want to check here

---

更正

阅读Joe的评论并重新阅读问题的详细信息，我想您想找到出现在同一短语中的所有单词以及指定列表中的所有单词.

Reading Joe's comment and re-reading the question details, I guess you want to find all words that appear in same phrase with ALL words in your specified list.

这看起来像是一个关系划分问题:

This looks like a relational division problem:

SELECT DISTINCT t2a.t1key
FROM t2 AS t2a
WHERE NOT EXISTS
  ( SELECT *
    FROM t2 AS t2b
    WHERE t2b.t1key IN (6,4)
      AND NOT EXISTS
      ( SELECT *
        FROM t2 AS t2c
        WHERE t2a.t3key = t2c.t3key
          AND t2c.t1key = t2b.t1key
      )
  )

第二种解决方法:

SELECT a.t1key
FROM t2 AS a
  JOIN t2 as b
    ON  a.t3key = b.t3key
WHERE b.t1key IN (6,4)       --list you want to check
GROUP BY a.t1key, a.t3key
HAVING COUNT(*) = 2          --size of list
;

第三个解决方案:

SELECT DISTINCT t1key
FROM t2
WHERE t3key IN
  ( SELECT t3key
    FROM t2
    WHERE t1key IN (6,4)
    GROUP BY t3key
    HAVING COUNT(*) = 2
  )
;

注意:第一个(使用NON EXISTS)解决方案与其他两个解决方案有很大不同:

Note: The first (with NON EXISTS) solution has a great difference with the other two:

如果您尝试使用其成员未出现在表t2中的列表(例如(2)或(2,7))进行尝试，它将显示t2中的所有t1密钥.

If you try it with a list that its members do not appear in table t2, say (2) or (2,7), it will show ALL t1key's from t2.

在这种情况下，第二个和第三个解决方案将根本不显示任何键.

The 2nd and 3rd solutions will show NO keys at all in such a case.

这篇关于有没有办法在这种类型的SQL SELECT中删除嵌套查询?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！