mysql 一次更新(update)多条记录的思路

UPDATE table_name 
SET field_name = CASE other_field 
WHEN 1 THEN 'value' 
WHEN 2 THEN 'value' 
WHEN 3 THEN 'value' 
END 
WHERE id IN (1,2,3)
测试代码如下：
<?php 
/* 
*function: insert app's apk ,logo_url, document_title,app_desc,package_name 
* into talbe atable use database db . 
*/ 

//connect database catx. 
$server='localhost'; 
$user='root'; 
$passwd='root'; 
$port='3306'; 
$dbname='catx'; 
$link=mysql_connect($server,$user,$passwd); 
if (!$link) { 
die('Could not connect: ' . mysql_error()); 
} 
else echo "Connected successfully\n"; 
mysql_select_db("db",$link); 
//set init variable and start time 
$st=microtime_float(); 
$table="pydot_g"; 
$path = "txt"; 
$fname_package_name = "package_name.txt"; 
// 
$handle= @fopen($path."/".$fname_package_name, "r"); 
$i=1; 
$sql = "UPDATE pydot_g SET package_name = CASE id "; 
$ids=""; 
while(($buf[$i]=fgets($handle,512))!==false){ 
$sql .= sprintf("WHEN %d THEN '%s' ", $i, $buf[$i]); // 拼接SQL语句 
$ids .= sprintf("%d,",$i); 
$i++; 
} 
//$ids=implode(',',$ids); 
$ids.=$i; 
$sql .= "END WHERE id IN ($ids)"; 
echo $sql; 
mysql_query($sql); 
fclose($handle); 
mysql_close($link); 
//echo the results and total time used 
$et=microtime_float(); 
$t=$et-$st; 
echo "\r\ninsert into talbe ",$table," ",$i,"times;\r\n"; 
echo "Total time $t seconds.\r\n"; 
//function calculate time ,return a float number 
function microtime_float(){ 
list($usec, $sec) = explode(" ", microtime()); 
return ((float)$usec + (float)$sec); 
} 
?>