MySQL優化以避免表掃描

Question

請考慮下表：

_____________________
|   sentence_word   |
|---------|---------|
| sent_id | word_id |
|---------|---------|
| 1       | 1       |
| 1       | 2       |
| ...     | ...     |
| 2       | 4       |
| 2       | 1       |
| ...     | ...     |

通過這種表結構，我想存儲句子中的單詞。 現在，我想找出句子中哪些單詞與特定單詞一起出現。 結果應如下所示：

_____________________
| word_id | counted |
|---------|---------|
| 5       | 1000    |
| 7       | 800     |
| 3       | 600     |
| 1       | 400     |
| 2       | 100     |
| ...     | ...     |

該查詢如下所示：

SELECT
    word_id,
    COUNT(*) AS counted
FROM sentence_word
WHERE sentence_word.sent_id IN (SELECT
    sent_id
    FROM sentence_word
    WHERE word_id = [desired word]
)
AND word_id != [desired word]
GROUP BY word_id
ORDER BY counted DESC;

查詢正在正常工作，但它始終掃描整個表。 我為send_id和word_id創建了一個索引。 您是否有什么想法可以對其進行優化，使其不需要一直掃描整個表？

Answer 1

您可以嘗試這樣的自我加入：

SELECT COUNT(DISTINCT sw1.word_id)
FROM sentence_word sw1
JOIN sentence_word sw2 ON (
    sw1.sent_id = sw2.sent_id
    AND sw2.word_id = [your word id]
)
WHERE sw1.word_id != [your word id]

甚至更好

SELECT COUNT(DISTINCT sw1.word_id)
FROM sentence_word sw1
JOIN sentence_word sw2 ON (
    sw1.sent_id = sw2.sent_id
    AND sw2.word_id = [your word id]
    AND sw2.word_id != sw1.word_id
)