mysql批量更新多条记录的同一个字段为不同值的方法

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;

1. 【replace into】和【insert into】更新都依赖于主键或唯一值，并都可能造成新增记录的操作的结构隐患
   
2. 【replace into】操作本质是对重复记录先delete然后insert，如果更新的字段不全缺失的字段将被设置成缺省值
   
3. 【insert into】则只是update重复的记录，更改的字段只能依循公式值
   
4. 【临时表】方式需要用户有temporary 表的create 权限
   
5.  数量较少时【replace into】和【insert into】性能最好，数量大时【临时表】最好，【case】则具有通用型也不具结构隐患

总结

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