Question

我有一个包含3列的表：id，句子和语言。所以句子可以是英语和德语，ID分配给具有相同含义但语言不同的句子，如

ID | sentence | language
1  | Hello    | en
1  | Hallo    | de
2  | Sorry    | en

可能只有一种语言存在句子。现在我想找出所有可用两种语言的句子，我可以用：

SELECT 
    *
FROM
    `sentences`
WHERE
    LENGTH(sentence) > 0
        AND (language = 'en' OR language = 'de')
GROUP BY id
HAVING COUNT(language) = 2

我只用德语得到句子的结果。然后我做

SELECT 
    *
FROM
    sentences
WHERE
    id IN (SELECT 
            id
        FROM
            `sentences`
        WHERE
            LENGTH(sentence) > 0
                AND (language = 'en' OR language = 'de')
        GROUP BY id
        HAVING COUNT(language) = 2)

这应该有效，但查询需要永远。我的问题：有没有任何奇特的方法可以做到这一点？

Answer 1

INNER JOINS比使用IN子句

更快

SELECT en.id, 
       en.sentence as en_sentence,
       de.sentence as de_sentence,
       en.language as en_language,
       de.language as de_language
FROM sentences en
INNER JOIN sentences de ON en.ID = de.ID AND en.language = 'en' AND de.language = 'de'
WHERE length(en.sentence) > 0
AND length(de.sentence) > 0

Answer 2

如果您的数据允许，请删除长度为0的句子。运行前备份：

DELETE FROM sentences WHERE LENGTH(SENTENCE) = 0

取出选择*，并获得您想要的一切。如果您没有索引，请在语言和ID上添加组合索引。

这将离开你

SELECT 
    ID, sentence, language.
FROM
    `sentences`
WHERE
    language = 'en' OR language = 'de'
GROUP BY id
HAVING COUNT(language) = 2

通过拥有组的Mysql查询

2 个答案: