實例測試Mysql使用索引帶來的效率提升 創建數據庫: [sql] CREATE DATABASE `sql_learn_db`; www.2cto.com 創建一個表: [sql] Create Table: CREATE TABLE `persons` ( `Id` int(11) NOT NULL AUTO_INCREMENT, `LastName` varchar(255) DEFAULT NULL, `FirstName` varchar(255) DEFAULT NULL, `Address` varchar(255) DEFAULT NULL, `City` varchar(255) DEFAULT NULL, PRIMARY KEY (`Id`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 表的結構: www.2cto.com [plain] +-----------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-----------+--------------+------+-----+---------+----------------+ | Id | int(11) | NO | PRI | NULL | auto_increment | | LastName | varchar(255) | YES | | NULL | | | FirstName | varchar(255) | YES | | NULL | | | Address | varchar(255) | YES | | NULL | | | City | varchar(255) | YES | | NULL | | +-----------+--------------+------+-----+---------+----------------+ 利用JDBC插入 1000000條數據。 DBIndexTest.java: (請手動修改用戶名和密碼,並導入驅動包) [java] import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.SQLException; import java.util.Random; public class DBIndexTest { private static final String MYSQL_DRIVER = "com.mysql.jdbc.Driver"; private static final String DB_URL = "jdbc:mysql://localhost:3306/sql_learn_db"; private static final String USER_NAME = "root"; private static final String PASSWORD = ""; private static final String sql = "insert into persons values (null,?,?,'zjut','hangzhou')"; private static Connection conn = null; private static PreparedStatement pstmt = null; private static Random random = new Random(); private DBIndexTest(){}; public static String getRandomName() { int fornum = 1 + random.nextInt(10); /* 1~10 */ StringBuilder sb = new StringBuilder(); /* 97~122 */ for(int i=0; i<fornum;i++) { sb.append((char)(97 + random.nextInt(26))); } return sb.toString(); } private static void createConnection() { try { Class.forName(MYSQL_DRIVER); conn = DriverManager.getConnection(DB_URL,USER_NAME,PASSWORD); } catch (ClassNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static Connection getConnection() { if(conn == null) { createConnection(); } return conn; } public static void insertRecord() { conn = getConnection(); try { if(pstmt == null) pstmt = conn.prepareStatement(sql); pstmt.setString(1, getRandomName()); pstmt.setString(2, getRandomName()); int affect = pstmt.executeUpdate(); System.out.println(affect == 1 ? "插入成功!" : "插入失敗!"); } catch (SQLException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public static void main(String[] args) { long start = System.currentTimeMillis(); for(int i=0; i< 1000000; i++) { insertRecord(); } long end = System.currentTimeMillis(); System.out.println("一共用時:" + (end-start)/1000.0 + "s"); } } 運行結果: [plain] 插入成功! 插入成功! 插入成功! ... ... ... 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 插入成功! 一共用時:2167.19s 表中已插入的記錄數: [sql] mysql> select count(*) from persons; +----------+ | count(*) | +----------+ | 1000000 | +----------+ 在沒有對表的列LastName建立索引時,嘗試查詢: [sql] mysql> select count(*) from persons where lastname='abc'; +----------+ | count(*) | +----------+ | 7 | +----------+ 1 row in set (6.33 sec) 對表列LastName建立索引: [sql] mysql> create index my_index on persons(lastname); Query OK, 0 rows affected (12.44 sec) Records: 0 Duplicates: 0 Warnings: 0 再次執行相同的查詢: www.2cto.com [sql] mysql> select count(*) from persons where lastname='abc'; +----------+ | count(*) | +----------+ | 7 | +----------+ 1 row in set (0.00 sec) 當然,0.00 sec 不等於0,因為速度太快,單位太大(秒),四捨五入後導致該結果(換成毫秒可能就不為0了)。 而且每次執行的結果也不一定相同。但是通過這個小小的實驗可以看出,使用索引的表比不使用索引的表要快一點,不過並不是絕對的。要不要使用索引技術要根據具體問題具體分析。如果某個表的查詢次數比較多,那麼就應該增加索引。但是索引會相應地使表更新速度下降(因為索引也要同時更新)。