Mysql查詢性能很慢，需要優化幫助

Question

我有4個表：發貨（200K記錄），商店（45記錄），product_stores（8K記錄），區（698記錄）。 以下查詢需要很長時間才能執行（12秒）：

SELECT `s`. * , `p`.`productCode` , `p`.`productName` , `st`.`name` AS `storeName` , `d`.`name` AS `districtName`
FROM `shipments` AS `s`
JOIN `product_stores` AS `p` ON s.productStoreId = p.id
JOIN `stores` AS `st` ON s.storeId = st.id
LEFT JOIN `districts` AS `d` ON s.districtId = d.id
WHERE (s.storeId IN (1, 2, 3, 4, 6, 9, 14, 16, 22, 26, 30))
GROUP BY `s`.`id`
ORDER BY `s`.`id` DESC
LIMIT 100

EXPLAIN查詢返回以下結果：

id  select_type     table   type    possible_keys   key     key_len     ref     rows    Extra
1   SIMPLE  st  ALL     PRIMARY     NULL    NULL    NULL    45  Using where; Using temporary; Using filesort
1   SIMPLE  s   ref     fk_shipments_stores1_idx,fk_shipments_product_stor...   fk_shipments_stores1_idx    4   st.id   482     
1   SIMPLE  p   eq_ref  PRIMARY     PRIMARY     4   s.productStoreId    1   
1   SIMPLE  d   eq_ref  PRIMARY     PRIMARY     4   s.districtId    1   

1. 我不知道為什么mysql必須使用臨時; 在這種情況下使用filesort
2. 為什么mysql無法從發貨中選擇？ 然后加入商店。 它從商店開始選擇然后加入貨物？ 我嘗試運行EXPLAIN，有時mysql從表product_stores開始選擇
3. 請幫我優化表，索引......以提高性能。

（我使用的是mysql 5.0.95）

這是表結構：

Answer 1

您的查詢將足夠慢，因為您的查詢加入策略需要太多的I / O.

讓我為您的查詢I / O草擬計算，以便理解如下：

 1. JOIN shipments (200K records) and product_stores (8K records) 

         200K x 8 K = 1600K I/O
 2. Then, JOIN to stores (45 records)

         1600K x 45 = 75000K I/O

 3. Then, JOIN to districts (698 records)

         75000K x 698 = 50256000K I/O

 4. Then, Filter the result (by storeId), so need to read the result I/O again

         50256000K + 50256000K = **100512000K I/O (TOTAL I/O)** 

 So, total I/O on memory of your query is 100512000K I/O. 

---

要提高查詢效果，您需要重新考慮您的查詢加入計划/策略

例如：

 1. Read shipments (200K records) and Filter storeId  (assume: result is 8 record)

         200K  + 8 = 208K I/O
 2. Then, JOIN to product_stores (8K records)

         208K x 8K = 1664K I/O

 3. Then, JOIN to stores (45 records)

         1664K x 45K = 74880K I/O

 4. Then, finally JOIN to districts (698 records).

         74880K + 698 = **52266240 I/O (TOTAL I/O)** 

 So, total I/O on memory of your query is 52266240  I/O. (greatly reduce I/O then ever)

因此，您可以通過以上方式提高查詢性能。

我希望它可以幫助你。

Answer 2

我只是在嘗試解決方案。 希望這可以減少執行時間

SELECT `s`. * , `ps`.`productCode` , `ps`.`productName` , `st`.`name` AS `storeName` , `d`.`name` AS `shipToDistrictName`
FROM `shipments` AS `s`
JOIN `product_stores` AS `ps` ON s.productStoreId = ps.id
JOIN `stores` AS `st` ON (s.storeId = st.id AND s.storeId IN (1, 2, 3, 4, 6, 9, 14, 16, 22, 26, 30))
LEFT JOIN `districts` AS `d` ON s.shipToDistrictId = d.id
GROUP BY `s`.`id`
ORDER BY `s`.`id` DESC
LIMIT 100

這將限制記錄的數量僅限於那些只有那些需要的記錄，並進一步與減少的記錄數連接，從而減少執行時間。

希望能幫助到你...