为防止主键冲突,设计DB的时候常常使用自增加(auto_increment 型)字段。因此插入数据前往往不知道改记录的主键是什么,为了方便后续或级联查询,我们需要在插入一行记录后获得DB自动生成的主键。这里稍微整理了下几种方法:
<p><span><strong>通用:</strong></span></p> <pre class="code"><span>SELECT</span> <span>max</span>(id) <span>FROM</span> <span>user</span>;
这个方法的缺点是不适合高并发。如果同时插入的时候返回的值可能不准确。
MySQL:
<span>SELECT</span> LAST_INSERT_ID();
重点: 假如你使用一条INSERT语句插入多个行, LAST_INSERT_ID() 只返回插入的第一行数据时产生的值。其原因是这使依靠其它服务器复制同样的 INSERT语句变得简单。
MS-SQL SERVER:
<span>select</span> <span>@@IDENTITY</span>;
@@identity是表示的是最近一次向具有identity属性(即自增列)的表插入数据时对应的自增列的值,是系统定义的全局变量。一般系统定义的全局变量都是以@@开头,用户自定义变量以@开头。比如有个表A,它的自增列是id,当向A表插入一行数据后,如果插入数据后自增列的值自动增加至101,则通过select @@identity得到的值就是101。使用@@identity的前提是在进行insert操作后,执行select @@identity的时候连接没有关闭,否则得到的将是NULL值。
补充:
SCOPE_IDENTITY、IDENT_CURRENT 和 @@IDENTITY 在功能上相似,因为它们都返回插入到 IDENTITY 列中的值。
IDENT_CURRENT 不受作用域和会话的限制,而受限于指定的表。IDENT_CURRENT 返回为任何会话和作用域中的特定表所生成的值。有关更多信息,请参见 IDENT_CURRENT。
SCOPE_IDENTITY 和 @@IDENTITY 返回在当前会话中的任何表内所生成的最后一个标识值。但是,SCOPE_IDENTITY 只返回插入到当前作用域中的值;@@IDENTITY 不受限于特定的作用域。
<p><span><span><strong>PHP: mysql_insert_id(<em>connection</em>);</strong> or <strong>mysqli_insert_id(<em>connection</em>)<em>;</em></strong></span></span></p> <p>参数 <em>connection</em> </p> <p>描述 必需。规定要使用的 MySQL 连接。</p> <pre class="code"><?<span>php </span><span>$con</span> = <span>mysql_connect</span>("localhost", "hello", "321"<span>); </span><span>if</span> (!<span>$con</span><span>) { </span><span>die</span>('Could not connect: ' . <span>mysql_error</span><span>()); } </span><span>$db_selected</span> = <span>mysql_select_db</span>("test_db",<span>$con</span><span>); </span><span>$sql</span> = "INSERT INTO person VALUES ('Carter','Thomas','Beijing')"<span>; </span><span>$result</span> = <span>mysql_query</span>(<span>$sql</span>,<span>$con</span><span>); </span><span>echo</span> "ID of last inserted record is: " . <span>mysql_insert_id</span><span>(); </span><span>mysql_close</span>(<span>$con</span><span>); </span>?>
<?<span>php </span><span>$con</span>=<span>mysqli_connect</span>("localhost","my_user","my_password","my_db"<span>); </span><span>//</span><span> Check connection</span> <span>if</span> (<span>mysqli_connect_errno</span>(<span>$con</span><span>)) { </span><span>echo</span> "Failed to connect to MySQL: " . <span>mysqli_connect_error</span><span>(); } </span><span>mysqli_query</span>(<span>$con</span>,"<span>INSERT INTO Persons (FirstName,LastName,Age) VALUES ('Glenn','Quagmire',33)</span>"<span>); </span><span>//</span><span> Print auto-generated id</span> <span>echo</span> "New record has id: " . <span>mysqli_insert_id</span>(<span>$con</span><span>); </span><span>mysqli_close</span>(<span>$con</span><span>); </span>?>
补充:
PHP-MySQL 是 PHP 操作 MySQL 资料库最原始的 Extension ,PHP-MySQLi 的 i 代表 Improvement ,提更了相对进阶的功能,就 Extension 而言,本身也增加了安全性。
a. mysql与mysqli的概念相关:
b. mysql与mysqli的区别:
c. mysql与mysqli的用法:
<span>$conn</span> = <span>mysql_connect</span>('localhost', 'user', 'password'); <span>//</span><span>连接mysql数据库</span> <span>mysql_select_db</span>('data_base'); <span>//</span><span>选择数据库</span> <span>$result</span> = <span>mysql_query</span>('select * from data_base');<span>//</span><span>第二个可选参数,指定打开的连接</span> <span>$row</span> = <span>mysql_fetch_row</span>( <span>$result</span> ) ) <span>//</span><span>只取一行数据</span> <span>echo</span> <span>$row</span>[0]; <span>//</span><span>输出第一个字段的值</span>
PS:mysqli以过程式的方式操作,有些函数必须指定资源,比如mysqli_query(资源标识,SQL语句),并且资源标识的参数是放在前面的,而mysql_query(SQL语句,'资源标识')的资源标识是可选的,默认值是上一个打开的连接或资源。
<span>$conn</span> = <span>new</span> mysqli('localhost', 'user', 'password','data_base'); <span>//</span><span>要使用new操作符,最后一个参数是直接指定数据库 //假如构造时候不指定,那下一句需要$conn -> select_db('data_base')实现</span> <span>$result</span> = <span>$conn</span> -> query( 'select * from data_base'<span> ); </span><span>$row</span> = <span>$result</span> -> fetch_row(); <span>//</span><span>取一行数据</span> <span>echo</span> row[0]; <span>//</span><span>输出第一个字段的值</span>
使用new mysqli('localhost', usenamer', 'password', 'databasename');会报错,提示如下:
Fatal error: Class 'mysqli' not found in ...
一般是mysqli是没有开启的,因为mysqli类不是默认开启的,win下要改php.ini,去掉php_mysqli.dll前的;,linux下要把mysqli编译进去。
d. mysql_connect()与mysqli_connect()
JDBC 2.0:insertRow()
Statement stmt = <span>null</span><span>; ResultSet rs </span>= <span>null</span><span>; </span><span>try</span><span> { stmt </span>= conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, <span>//</span><span> 创建Statement</span> <span> java.sql.ResultSet.CONCUR_UPDATABLE); stmt.executeUpdate(</span>"DROP TABLE IF EXISTS autoIncTutorial"<span>); stmt.executeUpdate( </span><span>//</span><span> 创建demo表</span> "CREATE TABLE autoIncTutorial (" + "priKey INT NOT NULL AUTO_INCREMENT, " + "dataField VARCHAR(64), PRIMARY KEY (priKey))"<span>); rs </span>= stmt.executeQuery("SELECT priKey, dataField " <span>//</span><span> 检索数据</span> + "FROM autoIncTutorial"<span>); rs.moveToInsertRow(); </span><span>//</span><span> 移动游标到待插入行(未创建的伪记录)</span> rs.updateString("dataField", "AUTO INCREMENT here?"); <span>//</span><span> 修改内容</span> rs.insertRow(); <span>//</span><span> 插入记录</span> rs.last(); <span>//</span><span> 移动游标到最后一行</span> <span>int</span> autoIncKeyFromRS = rs.getInt("priKey"); <span>//</span><span> 获取刚插入记录的主键preKey</span> <span> rs.close(); rs </span>= <span>null</span><span>; System.out.println(</span>"Key returned for inserted row: " +<span> autoIncKeyFromRS); } </span><span>finally</span><span> { </span><span>//</span><span> rs,stmt的close()清理</span> }
JDBC 3.0:getGeneratedKeys()
Statement stmt = <span>null</span><span>; ResultSet rs </span>= <span>null</span><span>; </span><span>try</span><span> { stmt </span>=<span> conn.createStatement(java.sql.ResultSet.TYPE_FORWARD_ONLY, java.sql.ResultSet.CONCUR_UPDATABLE); </span><span>//</span><span> ... </span><span>//</span><span> 省略若干行(如上例般创建demo表) </span><span>//</span><span> ...</span> <span> stmt.executeUpdate( </span>"INSERT INTO autoIncTutorial (dataField) " + "values ('Can I Get the Auto Increment Field?')"<span>, Statement.RETURN_GENERATED_KEYS); </span><span>//</span><span> 向驱动指明需要自动获取generatedKeys!</span> <span>int</span> autoIncKeyFromApi = -1<span>; rs </span>= stmt.getGeneratedKeys(); <span>//</span><span> 获取自增主键!</span> <span>if</span><span> (rs.next()) { autoIncKeyFromApi </span>= rs.getInt(1<span>); } </span><span>else</span><span> { </span><span>//</span><span> throw an exception from here</span> <span> } rs.close(); rs </span>= <span>null</span><span>; System.out.println(</span>"Key returned from getGeneratedKeys():" +<span> autoIncKeyFromApi); } </span><span>finally</span> { ... }