如何在 JDBC 中提交查询？
COMMIT命令用于将任何事务永久保存到数据库中。它用于结束您当前的事务并使事务中执行的所有更改永久化。事务是 Oracle 数据库将其视为一个单元的 SQL 语句序列。该语句还会擦除事务中的所有保存点并释放事务锁。
当我们使用任何 DML 命令如 INSERT、UPDATE 或 DELETE 时，这些命令所做的更改不是永久的，直到当前会话关闭，这些命令所做的更改才能回滚。为了避免这种情况，我们使用 COMMIT 命令将更改标记为永久。
使用JDBC API将我们的Java程序连接到 MySQL 服务器的 7 个步骤
- 导入包
- 加载并注册驱动程序
- 创建连接
- 创建声明
- 执行查询
- 处理结果
- 关闭连接
我们还需要在我们的项目中包含 MySQL 连接器。
提交的语法
COMMIT;
SQL Server 中用于创建相应 DB 和 Table 的 SQL 查询
创建数据库
CREATE DATABASE ;
当前数据库
use ;
在当前数据库中创建一个表
CREATE TABLE (usn int,, name varchar(20) , place varchar (20) );
例子
Java
// importing the my sql package
import java.sql.*;
/* The below code cannot generate the output here, since
* there is no connection between client and mysql server
*
* Before running the project in your device
* make SQL server connection with your project
* create the respective database/table in sql server
* in URL write the port number in which your mysql server
* is running (By default it run in port number 3306)
*/
public class GFG {
public static void main(String[] args)
{
// Database name
String databaseName = "student";
// Database URL
String url
= "jdbc:mysql://localhost:3306/" + databaseName;
// Database credentials
String userName = "root";
String password = "root";
Connection con = null;
Statement st = null;
ResultSet res = null;
String query = "";
try {
// Register the jdbc driver
Class.forName("com.mysql.jdbc.Driver");
// open a connection to database
con = DriverManager.getConnection(url, userName,
password);
// set auto commit false
con.setAutoCommit(false);
// creating statement
st = con.createStatement();
// first let us try to understand , how DB works
// without commit statement
query
= "INSERT INTO Student values ( 11 , 'Ram' , 'banglore' )";
// executing query 1 -> adding the above
// information into the table
st.executeUpdate(query);
System.out.println(
"Inserted row 1 FIRST TIME in the table....");
query
= "INSERT INTO Student values ( 22 , 'Shyam' , 'Chennai' )";
st.executeUpdate(query);
System.out.println(
"Inserted row 2 FIRST TIME in the table....");
// lets , print what we have updated in the table
query = "Select * from Student ; ";
res = st.executeQuery(query);
System.out.println(
"printing data (without Rollback && without Commit )....");
while (res.next())
System.out.print(res.getString("name")
+ " ");
System.out.println();
// lets try to rollback (undo the things ,till now we did)
// see what difference it will make in the Database
con.rollback();
// lets checkout our DB again
query = "Select * from Student";
res = st.executeQuery(query);
System.out.println(
"printing data (with Rollback && without Commit )....");
boolean empty = true;
while (res.next()) {
empty = false;
System.out.print(res.getString("name")
+ " ");
}
if (empty) {
System.out.println("Empty table\n\n");
}
// Since we haven't commited our transaction ,
// when we did rollback, everything is gone
// Now lets ,try with the Commit Statement from
// begining
query
= "INSERT INTO Student values ( 11 , 'Ram' , 'banglore' )";
st.executeUpdate(query);
System.out.println(
"Inserted row 1 SECOND TIME in the table....");
query
= "INSERT INTO Student values ( 22 , 'Shyam' , 'Chennai' )";
st.executeUpdate(query);
System.out.println(
"Inserted row 2 SECOND TIME in the table....");
// now we have committed our transaction
con.commit();
System.out.println(
"committed the transaction successfully....");
// lets rollback and like previous lets check
// what will be left in our database
con.rollback();
System.out.println("Done Rollback....");
query = "Select * from Student";
res = st.executeQuery(query);
System.out.println(
"printing data ( with Commit and then Rollback)....");
while (res.next())
System.out.print(res.getString("name")
+ " ");
System.out.println("\n");
}
catch (ClassNotFoundException e) {
System.out.println("Driver Error");
e.printStackTrace();
}
catch (SQLException e) {
System.out.println("Connection Error");
e.printStackTrace();
}
catch (Exception e) {
e.printStackTrace();
}
try {
// Clean-up environment
if (con != null)
con.close();
if (st != null)
con.close();
if (res != null)
res.close();
}
catch (Exception e) {
// Handle errors for JDBC
System.out.println(e.getMessage());
}
finally {
System.out.println("Thank you .........");
}
}
}输出
Inserted row 1 FIRST TIME in the table....
Inserted row 2 FIRST TIME in the table....
printing data (without Rollback && without Commit )....
Ram Shyam
printing data (with Rollback && without Commit )....
Empty table
Inserted row 1 SECOND TIME in the table....
Inserted row 2 SECOND TIME in the table....
committed the transaction successfully....
Done Rollback....
printing data ( with Commit and then Rollback)....
Ram Shyam
Thank you .........