使用臨時文件優化MySql查詢

Question

我有這個查詢（如下所示），其中當前使用臨時文件和文件夾爲了生成一組按順序結果分組。如果可能，我想擺脫他們的使用。我查看了這個查詢中使用的底層索引，我只是看不到缺少的內容。

SELECT 
    b.institutionid AS b__institutionid, 
    b.name AS b__name, 
    COUNT(DISTINCT f2.facebook_id) AS f2__0 
FROM education_institutions b 
LEFT JOIN facebook_education_matches f ON b.institutionid = f.institutionid 
LEFT JOIN facebook_education f2 ON f.school_uid = f2.school_uid 
WHERE 
    (
    b.approved = '1' 
    AND f2.facebook_id IN ([lots of facebook ids here ]) 
) 
GROUP BY b__institutionid 
ORDER BY f2__0 DESC 
LIMIT 10 

這裏是EXPLAIN EXTENDED輸出：

+----+-------------+-------+--------+--------------------------------+----------------+---------+----------------------------------+------+----------+----------------------------------------------+ 
| id | select_type | table | type | possible_keys     | key   | key_len | ref        | rows | filtered | Extra          | 
+----+-------------+-------+--------+--------------------------------+----------------+---------+----------------------------------+------+----------+----------------------------------------------+ 
| 1 | SIMPLE  | f  | index | PRIMARY,institutionId   | institutionId | 4  | NULL        | 308 | 100.00 | Using index; Using temporary; Using filesort | 
| 1 | SIMPLE  | f2 | ref | facebook_id_idx,school_uid_idx | school_uid_idx | 9  | f.school_uid      | 1 | 100.00 | Using where         | 
| 1 | SIMPLE  | b  | eq_ref | PRIMARY      | PRIMARY  | 4  | f.institutionId     | 1 | 100.00 | Using where         | 
+----+-------------+-------+--------+--------------------------------+----------------+---------+----------------------------------+------+----------+----------------------------------------------+ 

的CREATE TABLE語句爲每個表如下圖所示，讓你知道的模式。

CREATE TABLE facebook_education (
    education_id int(11) NOT NULL AUTO_INCREMENT, 
    name varchar(255) DEFAULT NULL, 
    school_uid bigint(20) DEFAULT NULL, 
    school_type varchar(255) DEFAULT NULL, 
    year smallint(6) DEFAULT NULL, 
    facebook_id bigint(20) DEFAULT NULL, 
    degree varchar(255) DEFAULT NULL, 
    PRIMARY KEY (education_id), 
    KEY facebook_id_idx (facebook_id), 
    KEY school_uid_idx (school_uid), 
    CONSTRAINT facebook_education_facebook_id_facebook_user_facebook_id FOREIGN KEY (facebook_id) REFERENCES facebook_user (facebook_id) 
) ENGINE=InnoDB AUTO_INCREMENT=484 DEFAULT CHARSET=utf8; 

CREATE TABLE facebook_education_matches (
    school_uid bigint(20) NOT NULL, 
    institutionId int(11) NOT NULL, 
    created_at timestamp NULL DEFAULT NULL, 
    updated_at timestamp NULL DEFAULT NULL ON UPDATE CURRENT_TIMESTAMP, 
    PRIMARY KEY (school_uid), 
    KEY institutionId (institutionId), 
    CONSTRAINT fk_facebook_education FOREIGN KEY (school_uid) REFERENCES facebook_education (school_uid) ON DELETE CASCADE ON UPDATE CASCADE, 
    CONSTRAINT fk_education_institutions FOREIGN KEY (institutionId) REFERENCES education_institutions (institutionId) ON DELETE CASCADE ON UPDATE CASCADE 
) ENGINE=InnoDB DEFAULT; 

CREATE TABLE education_institutions (
    institutionId int(11) NOT NULL AUTO_INCREMENT, 
    name varchar(100) NOT NULL, 
    type enum('School','Degree') DEFAULT NULL, 
    approved tinyint(1) NOT NULL DEFAULT '0', 
    deleted tinyint(1) NOT NULL DEFAULT '0', 
    normalisedName varchar(100) NOT NULL, 
    created_at timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP, 
    PRIMARY KEY (institutionId) 
) ENGINE=InnoDB AUTO_INCREMENT=101327 DEFAULT CHARSET=utf8; 

任何指導將不勝感激。

Answer 1

的文件排序很可能是因爲您對ORDER BY

它在MySQL "ORDER BY Optimization"文檔提到沒有合適的索引。

你可以做的是加載臨時表，然後從中選擇。加載臨時表時，請使用ORDER BY NULL。當您從臨時表中選擇時，請使用ORDER BY .. LIMIT

問題是該組添加隱含的order by <group by clause> ASC，除非通過添加order by null來禁用該行爲。
這是那些MySQL特定問題之一。

Answer 2

我可以看到兩個可能的優化，

1. b.approved =「1」 - 你絕對需要快速過濾覈准列的索引。

2. f2.facebook_id IN（[這裏有很多facebook的ids]） - 將facebook的id存儲在臨時表中。然後在臨時表上創建一個索引，然後與臨時表連接，而不是使用IN子句。