发布于 2017-01-05 21:28:24 | 145 次阅读 | 评论: 0 | 来源: 网友投递
Mysql关系型数据库管理系统
MySQL是一个开放源码的小型关联式数据库管理系统，开发者为瑞典MySQL AB公司。MySQL被广泛地应用在Internet上的中小型网站中。由于其体积小、速度快、总体拥有成本低，尤其是开放源码这一特点，许多中小型网站为了降低网站总体拥有成本而选择了MySQL作为网站数据库。
首先mysql更新数据的某个字段，一般这样写：
UPDATE mytable SET myfield = 'value' WHERE other_field = 'other_value';也可以这样用in指定要更新的记录：
UPDATE mytable SET myfield = 'value' WHERE other_field in ('other_values');这里注意 ‘other_values' 是一个逗号（，）分隔的字符串，如：1,2,3
如果更新多条数据而且每条记录要更新的值不同，可能很多人会这样写：
foreach ($values as $id => $myvalue) {
$sql = "UPDATE mytable SET myfield = $myvalue WHERE id = $id";
mysql_query($sql);
}即是循环一条一条的更新记录。一条记录update一次，这样性能很差，也很容易造成阻塞。
那么能不能一条sql语句实现批量更新呢？
mysql并没有提供直接的方法来实现批量更新，但是可以用点小技巧来实现。
UPDATE mytable
SET myfield = CASE id
WHEN 1 THEN 'myvalue1'
WHEN 2 THEN 'myvalue2'
WHEN 3 THEN 'myvalue3'
END
WHERE other_field ('other_values')如果where条件查询出记录的id不在CASE范围内，myfield将被设置为空。
如果更新多个值的话，只需要稍加修改：
UPDATE mytable
SET myfield1 = CASE id
WHEN 1 THEN 'myvalue11'
WHEN 2 THEN 'myvalue12'
WHEN 3 THEN 'myvalue13'
END,
myfield2 = CASE id
WHEN 1 THEN 'myvalue21'
WHEN 2 THEN 'myvalue22'
WHEN 3 THEN 'myvalue23'
END
WHERE id IN (1,2,3)这里以php为例，构造这两条mysql语句：
1、更新多条单个字段为不同值, mysql模式
$ids_values = array(
1 => 11,
2 => 22,
3 => 33,
4 => 44,
5 => 55,
6 => 66,
7 => 77,
8 => 88,
);
$ids = implode(',', array_keys($ids_values ));
$sql = "UPDATE mytable SET myfield = CASE id ";
foreach ($ids_values as $id=> $myvalue) {
$sql .= sprintf("WHEN %d THEN %d ", $id, $myvalue);
}
$sql .= "END WHERE id IN ($ids)";
echo $sql.";<br/>";输出：
UPDATE mytable SET myfield = CASE id WHEN 1 THEN 11 WHEN 2 THEN 22 WHEN 3 THEN 33 WHEN 4 THEN 44 WHEN 5 THEN 55 WHEN 6 THEN 66 WHEN 7 THEN 77 WHEN 8 THEN 88 END WHERE id IN (1,2,3,4,5,6,7,8);2、更新多个字段为不同值, PDO模式
$data = array(array('id' => 1, 'myfield1val' => 11, 'myfield2val' => 111), array('id' => 2, 'myfield1val' => 22, 'myfield2val' => 222));
$where_in_ids = implode(',', array_map(function($v) {return ":id_" . $v['id'];}, $data));
$update_sql = 'UPDATE mytable SET';
$params = array();
$update_sql .= ' myfield1 = CASE id';
foreach($data as $key => $item) {
$update_sql .= " WHEN :id_" . $key . " THEN :myfield1val_" . $key . " ";
$params[":id_" . $key] = $item['id'];
$params[":myfield1val_" . $key] = $item['myfield1val'];
}
$update_sql .= " END";
$update_sql .= ',myfield2 = CASE id';
foreach($data as $key => $item) {
$update_sql .= " WHEN :id_" . $key . " THEN :myfield2val_" . $key . " ";
$params[":id_" . $key] = $item['id'];
$params[":myfield1va2_" . $key] = $item['myfield2val'];
}
$update_sql .= " END";
$update_sql .= " WHERE id IN (" . $where_in_ids . ")";
echo $update_sql.";<br/>";
var_dump($params);输出：
UPDATE mytable SET myfield1 = CASE id WHEN :id_0 THEN :myfield1val_0 WHEN :id_1 THEN :myfield1val_1 END,myfield2 = CASE id WHEN :id_0 THEN :myfield2val_0 WHEN :id_1 THEN :myfield2val_1 END WHERE id IN (:id_1,:id_2);
array (size=6)
':id_0' => int 1
':myfield1val_0' => int 11
':id_1' => int 2
':myfield1val_1' => int 22
':myfield1va2_0' => int 111
':myfield1va2_1' => int 222另外三种批量更新方式
1. replace into 批量更新
replace into mytable(id, myfield) values (1,'value1'),(2,'value2'),(3,'value3');2. insert into ...on duplicate key update批量更新
insert into mytable(id, myfield1, myfield2) values (1,'value11','value21'),(2,'value12','value22'),(3,'value13','value23') on duplicate key update myfield1=values(myfield2),values(myfield2)+values(id);3. 临时表
DROP TABLE IF EXISTS `tmptable`;
create temporary table tmptable(id int(4) primary key,myfield varchar(50));
insert into tmptable values (1,'value1'),(2,'value2'),(3,'value3');
update mytable, tmptable set mytable.myfield = tmptable.myfield where mytable.id = tmptable.id;总结
以上就是这篇文章的全部内容了，希望本文的内容对大家的学习或者工作能带来一定的帮助，如果有疑问大家可以留言交流。