Question

我试图从两列中减去查询结果。

表：

 id |   word1   | lang1 |   word2   | lang2 |
----+-----------+-------+-----------+-------+
  1 | car       |   1   | car       |  15   |
  2 | table     |   1   | table     |  15   |
  3 | Chair     |   1   | cahair    |  13   |
  4 | CDplayer  |  15   | CDplayer  |   1   |
  5 | car       |   1   | car       |  13   |

我想在语言1中将word1中的所有单词转换为未翻译成语言12.所以在这种情况下它将是主席

表中有300万行，以下查询需要1分钟才能运行：

SELECT DISTINCT word1 
FROM `translations` 
WHERE lang1 = 1 
  AND lang2 != 15 
  AND NOT IN (SELECT word1 FROM `translations` WHERE lang2 == 15) 
LIMIT 10

分别对这两行进行选择是非常快的0.006s然后我可以在PHP中使用array_diff()来相互减去它们，但可能有一种更简单的方法直接在MySQL中进行。

Answer 1

SELECT 
    origin.word1
FROM 
    ( SELECT DISTINCT word1
      FROM tableX 
      WHERE lang1 = 1
    ) AS origin
WHERE 
    NOT EXISTS
      ( SELECT *
        FROM tableX AS trans
        WHERE trans.lang1 =  1
          AND trans.lang2 = 15
          AND trans.word1 = origin.word1
      ) ;

在运行这些查询之前，我会在(lang1, word1)上添加一个索引，在(lang1, lang2, word1) 上添加索引。

你也可以尝试这种变化（并检查两个解释计划）：

SELECT DISTINCT
      word1
FROM 
      tableX AS origin
WHERE 
      lang1 = 1
  AND 
      NOT EXISTS
      ( SELECT *
        FROM tableX AS trans
        WHERE trans.lang1 =  1
          AND trans.lang2 = 15
          AND trans.word1 = origin.word1
      ) ;

Answer 2

这应该很简单

SELECT
    m.id ,
    l.*
FROM mytable m
INNER JOIN (
            SELECT
                * 
            FROM mytable
            WHERE lang2 != 15
            GROUP BY id
) as l ON l.id = m.id
WHERE l.lang1 = 1
GROUP BY m.id

Answer 3

SELECT DISTINCT NonTranslated.word1
from
(SELECT DISTINCT word1 FROM `translations` WHERE lang1 = 1 AND lang2 != 15)NonTranslated
left join
(SELECT DISTINCT word1 FROM `translations` WHERE lang1 = 1 AND lang2 = 15)Translated
on NonTranslated.word1 = Translated.word1
where Translated.word1 is NULL;

让我知道这是什么解释。我认为它可能比选择子查询更快。

PS：假设：即使单词已翻译一次，也不会包含在列表中。

Answer 4

我不确定我是否完全理解这个问题。聚合是否有效？

select word1
from translations t
group by word1
having max(lang1 = 1) = 1 and
       max(lang2 = 15) = 0

减去mysql查询结果

4 个答案: