把百分号（%）符号替换成一个作为参数进行传递的变量：
<?php
$number = 2;
$str = "Shanghai";
$txt = sprintf("There are %u million cars in %s.",$number,$str);
echo $txt; // There are 2 million cars in Shanghai.
?>
经典代码案例：（经过删减之后有逻辑错误，只要本博主知道大体意思即可，其他人不要看该案例）
/**
*处理到期年份
* $tableid:字符串
* $where:筛选需要修改的档案的where条件
*/
public function updateExpireyear($idArr){
$emptyList = array();
$when = '';
$when_sql = "when %s then '%s' ";
$em_sql = "when %s then %s ";
foreach($docList as $k=>&$docone){
$tmp = sprintf($when_sql,$docone['id'],$docone['expireyear']);
$when = $when.$tmp;
}
if(!empty($emptyList)){
foreach($emptyList as $emone){
$emtmp = sprintf($em_sql,$emone['id'],$emone['expireyear']);
$when = $when.$emtmp;
}
}
$sql = "UPDATE {$tableid} SET `expireyear` = CASE id ".$when." END WHERE `id` in ({$ids}) ";
$result = $this->getProxy('db')->execute($sql);
}
传入参数：
array(1527844078575627623,1520502796098626275)
执行sql查询：
UPDATE f1_14_document SET `expireyear` = CASE id when 1520502796098626275 then '15' when 1527844078575627623 then '10' END WHERE `id` in (1520502796098626275,1527844078575627623)
这里使用sprintf 拼凑出了 “when 1520502796098626275 then '15' when 1527844078575627623 then '10'”