最近写了点关于将excel导入数据库的代码,当然也可以看做是对前面所介绍的小项目进行补充所做的准备。 我一般都是先完成功能,然后将其封装成块,再添加到项目中,个人癖好不得借鉴。 这是已经成功插入数据化数据库中数据的记录,我新建的表为db. 这是在控制
最近写了点关于将excel导入数据库的代码,当然也可以看做是对前面所介绍的小项目进行补充所做的准备。
我一般都是先完成功能,然后将其封装成块,再添加到项目中,个人癖好不值得借鉴。
这是已经成功插入数据化数据库中数据的记录,我新建的表为db. 这是在控制台的数据输入喎?http://www.2cto.com/kf/ware/vc/" target="_blank" class="keylink">vcD4KPHA+uty24MqxuvLGtL3T19a3+7Suyse63Lbgz+7Ev7HY0OvX9rXEo6y4w7T6wuvW0M7SxrS908HLsrvJ2XNxbNPvvuSjrNKy0O3T0Lj8vPK1pbXEt73KvaOstavKx87Sz9bU2ta7xNzP67W91eLSu7K9oaM8L3A+CjxwcmUgY2xhc3M9"brush:sql;">/**将execl数据导入数据库
* @author trsli
* */
public class CreateDBTable {
private static Connection conn;
private static String sql="";
private static StringBuffer buf=new StringBuffer();
static{
conn=DBConnection.getConnection();
}
public static void main(String[] args) {
//数据.xls文件路径
System.out.println("输入文件路径:");
String filename=new Scanner(System.in).nextLine();
//获取需要插入数据库的数据内容
Object[][] contents=new PoiUtil().getmessage(filename);
//获取数据库创建表格的字段名
Object[] titles=new PoiUtil().gettitles(filename);
System.out.println("输入数表格名:");
String fname=new Scanner(System.in).nextLine();
try {
String ziduan="";
String blank="";
PreparedStatement stmt=conn.prepareStatement(sql);
buf.append("create table "+fname+"( id int primary key auto_increment");
//拼接字符串,主要是为了完全实现动态创建数据表格以及后期插入数据
for(int i=0;i 整个代码很简单,可以从中提取出需要的方法,用于其它需要的地方。 这是数据库中数据的显示。 以下是原数据:

InnoDB uses redologs and undologs to ensure data consistency and reliability. 1.redologs record data page modification to ensure crash recovery and transaction persistence. 2.undologs records the original data value and supports transaction rollback and MVCC.

Key metrics for EXPLAIN commands include type, key, rows, and Extra. 1) The type reflects the access type of the query. The higher the value, the higher the efficiency, such as const is better than ALL. 2) The key displays the index used, and NULL indicates no index. 3) rows estimates the number of scanned rows, affecting query performance. 4) Extra provides additional information, such as Usingfilesort prompts that it needs to be optimized.

Usingtemporary indicates that the need to create temporary tables in MySQL queries, which are commonly found in ORDERBY using DISTINCT, GROUPBY, or non-indexed columns. You can avoid the occurrence of indexes and rewrite queries and improve query performance. Specifically, when Usingtemporary appears in EXPLAIN output, it means that MySQL needs to create temporary tables to handle queries. This usually occurs when: 1) deduplication or grouping when using DISTINCT or GROUPBY; 2) sort when ORDERBY contains non-index columns; 3) use complex subquery or join operations. Optimization methods include: 1) ORDERBY and GROUPB

MySQL/InnoDB supports four transaction isolation levels: ReadUncommitted, ReadCommitted, RepeatableRead and Serializable. 1.ReadUncommitted allows reading of uncommitted data, which may cause dirty reading. 2. ReadCommitted avoids dirty reading, but non-repeatable reading may occur. 3.RepeatableRead is the default level, avoiding dirty reading and non-repeatable reading, but phantom reading may occur. 4. Serializable avoids all concurrency problems but reduces concurrency. Choosing the appropriate isolation level requires balancing data consistency and performance requirements.

MySQL is suitable for web applications and content management systems and is popular for its open source, high performance and ease of use. 1) Compared with PostgreSQL, MySQL performs better in simple queries and high concurrent read operations. 2) Compared with Oracle, MySQL is more popular among small and medium-sized enterprises because of its open source and low cost. 3) Compared with Microsoft SQL Server, MySQL is more suitable for cross-platform applications. 4) Unlike MongoDB, MySQL is more suitable for structured data and transaction processing.

MySQL index cardinality has a significant impact on query performance: 1. High cardinality index can more effectively narrow the data range and improve query efficiency; 2. Low cardinality index may lead to full table scanning and reduce query performance; 3. In joint index, high cardinality sequences should be placed in front to optimize query.

The MySQL learning path includes basic knowledge, core concepts, usage examples, and optimization techniques. 1) Understand basic concepts such as tables, rows, columns, and SQL queries. 2) Learn the definition, working principles and advantages of MySQL. 3) Master basic CRUD operations and advanced usage, such as indexes and stored procedures. 4) Familiar with common error debugging and performance optimization suggestions, such as rational use of indexes and optimization queries. Through these steps, you will have a full grasp of the use and optimization of MySQL.

MySQL's real-world applications include basic database design and complex query optimization. 1) Basic usage: used to store and manage user data, such as inserting, querying, updating and deleting user information. 2) Advanced usage: Handle complex business logic, such as order and inventory management of e-commerce platforms. 3) Performance optimization: Improve performance by rationally using indexes, partition tables and query caches.


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