一、生成唯一uuid
二、生成唯一uid
三、生成唯一uid的正確方法
看到某些人會用uuid去代替用戶的uid
從代碼中可以看出,透過unique生成一個以毫秒級時間戳爲前綴的字元后md5加密
再透過分隔符進行分割後得到uuid
這種方式雖然極大程度的避免了uid的重複
但是生成的uid太長,足足36個字元,而且是混雜英文和數字元號的,可讀性很差
而一般的uid中都是純數值組成的
function generateUUid($strtoupper = false){ $charid = call_user_func($strtoupper ? 'strtoupper' : 'strtolower', md5(uniqid(microtime(true), true))); $hyphen = chr(45); $uuid = substr($charid, 0, 8) . $hyphen . substr($charid, 8, 4) . $hyphen . substr($charid, 12, 4) . $hyphen . substr($charid, 16, 4) . $hyphen . substr($charid, 20, 12); return $uuid;} //結果:37f14a07-cb18-2e54-4e40-da1e2fa0456d
由於一般正常的uid都是純數值型的
而要保證唯一性,必然要跟時間戳有關係,因此有了以下代碼
爲了儘可能的在同一秒中註冊人數的uid不同,將時間戳進行打亂隨機排序,也不失爲一個好辦法
但是這種缺點就是,uid長度是固定的,無法進行改變,雖然呢,打亂字元是一個很好的解決重複的方式
但是事情無絕對,如果真的因爲隨機碰撞導致的uid相同該如何
爲了更保險起見,必然還是要走一次數據庫的查詢
大大增加了數據庫的I/O壓力
function generateUid(){ return call_user_func('str_shuffle', time());} //結果:4067524162
雖然說上面的兩種方式並非不可取
但是在大型公司必然不可取,一種是uid的格式必然純數值,所以uuid方式可以排除
另外由於對數據庫的壓力起見,必然也不會採用第二種方式
而最經常採用的方式應該是使用數據庫的主鍵索引,因爲主鍵索引必然唯一
這裏很多人會疑惑,主鍵索引不是會從1開始嗎,這uid會有1位數的?
小了,格局小了,你可以設定主鍵索引的offset,讓他從100000開始,不就可以解決這個問題了嗎
這時候有人又問,那主鍵索引增加不是有規律的嗎,比如插一條,會自增1
這時候就可以設定主鍵索引的增長步長,讓他插入一條的步長不爲1即可
而爲了讓uid看起來更加沒有關聯性,你可以設定步長爲基數,比如3
這樣增長起來,就會是100000,100003,100006,100009,100012....
php中生成標準uuid的方法
UUID是指在一臺機器上生成的數字,它保證對在同一時空中的所有機器都是唯一的。
通常平臺 會提供生成UUID的API。UUID按照開放軟件基金會(OSF)制定的標準計算,用到了以太網卡地址、納秒級時間、芯片ID碼和許多可能的數字。
由以 下幾部分的組合:當前日期和時間(UUID的第一個部分與時間有關,如果你在生成一個UUID之後,過幾秒又生成一個UUID,則第一個部分不同,其餘相 同),時鐘序列,全局唯一的IEEE機器識別號(如果有網卡,從網卡獲得,沒有網卡以其他方式獲得),UUID的唯一缺陷在於生成的結果串會比較長。
關於 UUID這個標準使用最普遍的是微軟的GUID(Globals Unique Identifiers)。
在ColdFusion中可以用CreateUUID()函數很簡單的生成UUID,其格式爲:xxxxxxxx-xxxx-xxxx- xxxxxxxxxxxxxxxx(8-4-4-16),其中每個 x 是 0-9 或 a-f 範圍內的一個十六進制的數字。
而標準的UUID格式爲:xxxxxxxx-xxxx-xxxx-xxxxxx-xxxxxxxxxx (8-4-4-4-12)
function guid(){ if (function_exists('com_create_guid')){ return com_create_guid(); }else{ mt_srand((double)microtime()*10000);//optional for php 4.2.0 and up. $charid = strtoupper(md5(uniqid(rand(), true))); $hyphen = chr(45);// "-" $uuid = chr(123)// "{" .substr($charid, 0, 8).$hyphen .substr($charid, 8, 4).$hyphen .substr($charid,12, 4).$hyphen .substr($charid,16, 4).$hyphen .substr($charid,20,12) .chr(125);// "}" return $uuid; }}echo guid();?>
到此這篇關於php生成唯一uid的解決方法詳解的文章就介紹到這了。
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