從概念上講,我試圖爲系統中的每個用戶獲取8個單獨的調查分數。我想輸出連接到同一行輸出的給定用戶的所有8個分數。這是我的最佳實現:MySQL查詢優化消除不必要的連接
SELECT cp.CONSUMER_ID,
bsr1.SCORE AS SET_1_SCORE,
bsr2.SCORE AS SET_2_SCORE,
bsr3.SCORE AS SET_3_SCORE,
bsr4.SCORE AS SET_4_SCORE,
bsr5.SCORE AS SET_5_SCORE,
bsr6.SCORE AS SET_6_SCORE,
bsr7.SCORE AS SET_7_SCORE,
bsr8.SCORE AS SET_8_SCORE
FROM
CONSUMER_PROFILE AS cp
LEFT JOIN survey_scores AS bsr1
ON bsr1.SET_ORDER=1
AND bsr1.CUSTOMER_ID=cp.CONSUMER_ID
LEFT JOIN survey_scores AS bsr2
ON bsr2.SET_ORDER=2
AND bsr2.CUSTOMER_ID=cp.CONSUMER_ID
LEFT JOIN survey_scores AS bsr3
ON bsr3.SET_ORDER=3
AND bsr3.CUSTOMER_ID=cp.CONSUMER_ID
LEFT JOIN survey_scores AS bsr4
ON bsr4.SET_ORDER=4
AND bsr4.CUSTOMER_ID=cp.CONSUMER_ID
LEFT JOIN survey_scores AS bsr5
ON bsr5.SET_ORDER=5
AND bsr5.CUSTOMER_ID=cp.CONSUMER_ID
LEFT JOIN survey_scores AS bsr6
ON bsr6.SET_ORDER=6
AND bsr6.CUSTOMER_ID=cp.CONSUMER_ID
LEFT JOIN survey_scores AS bsr7
ON bsr7.SET_ORDER=7
AND bsr7.CUSTOMER_ID=cp.CONSUMER_ID
LEFT JOIN survey_scores AS bsr8
ON bsr8.SET_ORDER=8
AND bsr8.CUSTOMER_ID=cp.CONSUMER_ID
這將返回正確的輸出,但速度非常慢。你會如何建議我優化它?
請發佈'EXPLAIN'輸出。 – derobert 2011-03-08 21:58:47