我有一个表与以下字段:
id (Unique)
url (Unique)
title
company
site_id
现在，我需要删除具有相同标题、company和site_id的行。一种方法是使用下面的SQL和脚本(PHP):
SELECT title, site_id, location, id, count( * )
FROM jobs
GROUP BY site_id, company, title, location
HAVING count( * ) >1
运行此查询后，可以使用服务器端脚本删除重复项。
但是，我想知道这是否只能使用SQL查询。
当前回答
如果不想更改列属性，那么可以使用下面的查询。
因为你有一个列，它有唯一的id(例如，auto_increment列)，你可以用它来删除重复项:
DELETE `a`
FROM
`jobs` AS `a`,
`jobs` AS `b`
WHERE
-- IMPORTANT: Ensures one version remains
-- Change "ID" to your unique column's name
`a`.`ID` < `b`.`ID`
-- Any duplicates you want to check for
AND (`a`.`title` = `b`.`title` OR `a`.`title` IS NULL AND `b`.`title` IS NULL)
AND (`a`.`company` = `b`.`company` OR `a`.`company` IS NULL AND `b`.`company` IS NULL)
AND (`a`.`site_id` = `b`.`site_id` OR `a`.`site_id` IS NULL AND `b`.`site_id` IS NULL);
在MySQL中，你可以用空安全的相等操作符(又名“宇宙飞船操作符”)来简化它:
DELETE `a`
FROM
`jobs` AS `a`,
`jobs` AS `b`
WHERE
-- IMPORTANT: Ensures one version remains
-- Change "ID" to your unique column's name
`a`.`ID` < `b`.`ID`
-- Any duplicates you want to check for
AND `a`.`title` <=> `b`.`title`
AND `a`.`company` <=> `b`.`company`
AND `a`.`site_id` <=> `b`.`site_id`;
其他回答
简单和快速的所有情况:
CREATE TEMPORARY TABLE IF NOT EXISTS _temp_duplicates AS (SELECT dub.id FROM table_with_duplications dub GROUP BY dub.field_must_be_uniq_1, dub.field_must_be_uniq_2 HAVING COUNT(*) > 1);
DELETE FROM table_with_duplications WHERE id IN (SELECT id FROM _temp_duplicates);
如果不想更改列属性，那么可以使用下面的查询。
因为你有一个列，它有唯一的id(例如，auto_increment列)，你可以用它来删除重复项:
DELETE `a`
FROM
`jobs` AS `a`,
`jobs` AS `b`
WHERE
-- IMPORTANT: Ensures one version remains
-- Change "ID" to your unique column's name
`a`.`ID` < `b`.`ID`
-- Any duplicates you want to check for
AND (`a`.`title` = `b`.`title` OR `a`.`title` IS NULL AND `b`.`title` IS NULL)
AND (`a`.`company` = `b`.`company` OR `a`.`company` IS NULL AND `b`.`company` IS NULL)
AND (`a`.`site_id` = `b`.`site_id` OR `a`.`site_id` IS NULL AND `b`.`site_id` IS NULL);
在MySQL中，你可以用空安全的相等操作符(又名“宇宙飞船操作符”)来简化它:
DELETE `a`
FROM
`jobs` AS `a`,
`jobs` AS `b`
WHERE
-- IMPORTANT: Ensures one version remains
-- Change "ID" to your unique column's name
`a`.`ID` < `b`.`ID`
-- Any duplicates you want to check for
AND `a`.`title` <=> `b`.`title`
AND `a`.`company` <=> `b`.`company`
AND `a`.`site_id` <=> `b`.`site_id`;
你可以很容易地从这个代码中删除重复的记录。
$qry = mysql_query("SELECT * from cities");
while($qry_row = mysql_fetch_array($qry))
{
$qry2 = mysql_query("SELECT * from cities2 where city = '".$qry_row['city']."'");
if(mysql_num_rows($qry2) > 1){
while($row = mysql_fetch_array($qry2)){
$city_arry[] = $row;
}
$total = sizeof($city_arry) - 1;
for($i=1; $i<=$total; $i++){
mysql_query( "delete from cities2 where town_id = '".$city_arry[$i][0]."'");
}
}
//exit;
}
我必须对文本字段执行此操作，并且遇到了索引上100字节的限制。
我通过添加一个列来解决这个问题，对字段进行md5哈希，并进行更改。
ALTER TABLE table ADD `merged` VARCHAR( 40 ) NOT NULL ;
UPDATE TABLE SET merged` = MD5(CONCAT(`col1`, `col2`, `col3`))
ALTER IGNORE TABLE table ADD UNIQUE INDEX idx_name (`merged`);
如果IGNORE语句在我的例子中不起作用，你可以使用下面的语句:
CREATE TABLE your_table_deduped LIKE your_table;
INSERT your_table_deduped
SELECT *
FROM your_table
GROUP BY index1_id,
index2_id;
RENAME TABLE your_table TO your_table_with_dupes;
RENAME TABLE your_table_deduped TO your_table;
#OPTIONAL
ALTER TABLE `your_table` ADD UNIQUE `unique_index` (`index1_id`, `index2_id`);
#OPTIONAL
DROP TABLE your_table_with_dupes;
