假设有一个名为contact
的表,其下一个结构为:
id INT -- primary key,autoincrement,index
firstname VARCHAR (255),
lastname VARCHAR(255),
type ENUM
执行此类查询:
SELECT c1.id AS c1_id, c2.id AS c2_id
FROM contact c1
INNER JOIN contact c2 ON c1.firstname = c2.firstname AND c1.lastname = c2.lastname
WHERE c1.id <> c2.id AND c1.type=c2.type
在一小部分记录上没问题......但是当记录数从30-40增加到1000时,这个查询非常慢。需要从记录计数中抽象出来并尽可能加快这个查询的最大速度。任何建议?
答案 0 :(得分:4)
你可以尝试这样的事情:
SELECT GROUP_CONCAT(DISTINCT id), firstname, lastname
FROM contact
GROUP BY firstname, lastname
HAVING COUNT(DISTINCT id)>1
这将返回所有重复的名称。如果你想要ID,那么你可以使用JOIN:
SELECT
contact.id
FROM
contact INNER JOIN (SELECT firstname, lastname
FROM contact
GROUP BY firstname, lastname
HAVING COUNT(DISTINCT id)>1) dup
ON contact.firstname=dup.firstname AND contact.lastname=dup.lastname
答案 1 :(得分:1)
与fthiella的回答略有偏差(只是这就是你所需要的):
SELECT group_concat(id) as ids, firstname, lastname
FROM contact
GROUP BY firstname, lastname
上面的查询将使用逗号分隔的每个名字+姓氏组合的id列表填充列ID。
答案 2 :(得分:1)
除了“&lt;&gt;”之外,您的查询很好(实际上,它甚至可能比提出的替代方案快一点!)。这只是你的索引需要一些工作......
CREATE TABLE contact
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,firstname VARCHAR(255) NOT NULL
,lastname VARCHAR(255) NOT NULL
,type ENUM('small','medium','large') NOT NULL
);
INSERT INTO contact VALUES
(NULL,'John','Brown','small'),
(NULL,'Bill','Red','small'),
(NULL,'Paul','Orange','medium'),
(NULL,'Mike','Green','large'),
(NULL,'John','Scarlet','small'),
(NULL,'John','Cyan','medium'),
(NULL,'Fiona','Brown','large'),
(NULL,'John','Brown','small'),
(NULL,'Chris','Copper','medium'),
(NULL,'Steve','Silver','large');
INSERT INTO contact SELECT NULL,x.firstname, y.lastname, z.type FROM contact x, contact y, contact z;
SELECT COUNT(*) FROM contact;
+----------+
| COUNT(*) |
+----------+
| 1010 |
+----------+
1 row in set (0.01 sec)
SELECT c1.id c1_id
, c2.id c2_id
FROM contact c1
JOIN contact c2
ON c1.firstname = c2.firstname
AND c1.lastname = c2.lastname
AND c1.type=c2.type
WHERE c1.id < c2.id;
...
...
| 1006 | 1008 |
+-------+-------+
5634 rows in set (0.16 sec)
所以,现在让我们在(名字,姓氏,类型)...
上添加一个索引 DROP TABLE IF EXISTS contact;
CREATE TABLE contact
(id INT NOT NULL AUTO_INCREMENT PRIMARY KEY
,firstname VARCHAR(255) NOT NULL
,lastname VARCHAR(255) NOT NULL
,type ENUM('small','medium','large') NOT NULL
,INDEX(firstname,lastname,type)
);
INSERT INTO contact VALUES
(NULL,'John','Brown','small'),
(NULL,'Bill','Red','small'),
(NULL,'Paul','Orange','medium'),
(NULL,'Mike','Green','large'),
(NULL,'John','Scarlet','small'),
(NULL,'John','Cyan','medium'),
(NULL,'Fiona','Brown','large'),
(NULL,'John','Brown','small'),
(NULL,'Chris','Copper','medium'),
(NULL,'Steve','Silver','large');
INSERT INTO contact SELECT NULL,x.firstname, y.lastname, z.type FROM contact x, contact y, contact z;
SELECT c1.id c1_id
, c2.id c2_id
FROM contact c1
JOIN contact c2
ON c1.firstname = c2.firstname
AND c1.lastname = c2.lastname
AND c1.type = c2.type
AND c1.id < c2.id;
| 775 | 776 |
...
| 1006 | 1008 |
+-------+-------+
5634 rows in set (0.05 sec)