首先mysql更新數(shù)據(jù)的某個(gè)字段，一般這樣寫：
UPDATE mytable SET myfield = 'value' WHERE other_field = 'other_value';
也可以這樣用in指定要更新的記錄：
UPDATE mytable SET myfield = 'value' WHERE other_field in ('other_values');
這里注意 ‘other_values' 是一個(gè)逗號(hào)（，）分隔的字符串，如：1,2,3
如果更新多條數(shù)據(jù)而且每條記錄要更新的值不同，可能很多人會(huì)這樣寫：
foreach ($values as $id => $myvalue) {
$sql = "UPDATE mytable SET myfield = $myvalue WHERE id = $id";
mysql_query($sql);
}
即是循環(huán)一條一條的更新記錄。一條記錄update一次，這樣性能很差，也很容易造成阻塞。
那么能不能一條sql語(yǔ)句實(shí)現(xiàn)批量更新呢？
mysql并沒(méi)有提供直接的方法來(lái)實(shí)現(xiàn)批量更新，但是可以用點(diǎn)小技巧來(lái)實(shí)現(xiàn)。
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條件查詢出記錄的id不在CASE范圍內(nèi)，myfield將被設(shè)置為空。
如果更新多個(gè)值的話，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)
這里以php為例，構(gòu)造這兩條mysql語(yǔ)句：
1、更新多條單個(gè)字段為不同值, 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/>";
輸出：
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、更新多個(gè)字段為不同值, 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);
輸出：
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
另外三種批量更新方式
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. 臨時(shí)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;
- 【replace into】和【insert into】更新都依賴于主鍵或唯一值，并都可能造成新增記錄的操作的結(jié)構(gòu)隱患
- 【replace into】操作本質(zhì)是對(duì)重復(fù)記錄先delete然后insert，如果更新的字段不全缺失的字段將被設(shè)置成缺省值
- 【insert into】則只是update重復(fù)的記錄，更改的字段只能依循公式值
- 【臨時(shí)表】方式需要用戶有temporary 表的create 權(quán)限
- 數(shù)量較少時(shí)【replace into】和【insert into】性能最好，數(shù)量大時(shí)【臨時(shí)表】最好，【CASE】則具有通用型也不具結(jié)構(gòu)隱患
總結(jié)
以上就是這篇文章的全部?jī)?nèi)容了，希望本文的內(nèi)容對(duì)大家的學(xué)習(xí)或者工作能帶來(lái)一定的幫助，如果有疑問(wèn)大家可以留言交流。
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