package com.msit.Uitll;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
/**
* 数据库帮助类 连接MySQL数据库
*
* @author ruanj_000
*
*/
public class SQLHelp {
private static String dirverName = "com.mysql.jdbc.Driver";
private static String url = "jdbc:mysql://127.0.0.1:3306/misidb";
private static String user = "root";
private static String password = "root";
private static Connection connection = null;
// 编写静态代码块(比构造函数加载更快),用来加载驱动类
static {
try {
Class.forName(dirverName);
// 创建连接对象
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
/**
* 获得连接对象
*
* @return
*/
public static Connection getConnection() {
try {
connection = DriverManager.getConnection(url, user, password);
} catch (SQLException e) {
e.printStackTrace();
}
return connection;
}
/**
* 用来执行 添加、删除、修改的sql语句
*
* @param sql
* @return 受影响的行数
*/
public static int ExecuteNonQuery(String sql) {
int num = 0;
Connection conn = getConnection();
Statement sta = null;
try {
sta = conn.createStatement();
} catch (SQLException e) {
e.printStackTrace();
}
try {
num = sta.executeUpdate(sql);
} catch (SQLException e) {
e.printStackTrace();
} finally {
Close(null, sta, conn);
}
return num;
}
/**
* 执行查询语句方法
* @param sql 数据查询SQL脚本语言
* @return 返回结果集
*/
public static ResultSet ExecuteQuery(String sql){
ResultSet rs=null;
Connection con=getConnection();
Statement sta=null;
try {
sta=con.createStatement();
} catch (SQLException e) {
e.printStackTrace();
}
try {
rs=sta.executeQuery(sql);
} catch (SQLException e) {
e.printStackTrace();
}
finally{
//Close(rs, sta, con);
}
return rs;
}
/**
* 关闭资源的方法
*
* @param rs
* 结果集
* @param sta
* 执行对象
* @param conn
* 连接对象
*/
private static void Close(ResultSet rs, Statement sta, Connection conn) {
if (rs != null) {
try {
rs.close();
} catch (SQLException e) {
System.out.println("数据结果集关闭异常..!");
e.printStackTrace();
}
}
if (sta != null) {
try {
sta.close();
} catch (SQLException e) {
System.out.println("执行对象关闭异常、、!");
e.printStackTrace();
}
}
if (conn != null) {
try {
conn.close();
} catch (SQLException e) {
System.out.println("数据连接关闭异常、、!");
e.printStackTrace();
}
}
rs=null; sta=null; conn=null;
}
/**
* 执行预编译sql语句的方法
* @param sql
* @param prgm
* @return
*/
public static int pstm(String sql,String prgm[]){
int num=0;
PreparedStatement pstm=null;
try {
pstm =getConnection().prepareStatement(sql);
for (int i =1; i pstm.setString(i, prgm[i-1]);
}
num=pstm.executeUpdate();
pstm.close();
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
return num;
}
}

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MySQLstringtypesincludeVARCHAR,TEXT,CHAR,ENUM,andSET.1)VARCHARisversatileforvariable-lengthstringsuptoaspecifiedlimit.2)TEXTisidealforlargetextstoragewithoutadefinedlength.3)CHARisfixed-length,suitableforconsistentdatalikecodes.4)ENUMenforcesdatainte

MySQLoffersvariousstringdatatypes:1)CHARforfixed-lengthstrings,2)VARCHARforvariable-lengthtext,3)BINARYandVARBINARYforbinarydata,4)BLOBandTEXTforlargedata,and5)ENUMandSETforcontrolledinput.Eachtypehasspecificusesandperformancecharacteristics,sochoose

TograntpermissionstonewMySQLusers,followthesesteps:1)AccessMySQLasauserwithsufficientprivileges,2)CreateanewuserwiththeCREATEUSERcommand,3)UsetheGRANTcommandtospecifypermissionslikeSELECT,INSERT,UPDATE,orALLPRIVILEGESonspecificdatabasesortables,and4)

ToaddusersinMySQLeffectivelyandsecurely,followthesesteps:1)UsetheCREATEUSERstatementtoaddanewuser,specifyingthehostandastrongpassword.2)GrantnecessaryprivilegesusingtheGRANTstatement,adheringtotheprincipleofleastprivilege.3)Implementsecuritymeasuresl

ToaddanewuserwithcomplexpermissionsinMySQL,followthesesteps:1)CreatetheuserwithCREATEUSER'newuser'@'localhost'IDENTIFIEDBY'password';.2)Grantreadaccesstoalltablesin'mydatabase'withGRANTSELECTONmydatabase.TO'newuser'@'localhost';.3)Grantwriteaccessto'

The string data types in MySQL include CHAR, VARCHAR, BINARY, VARBINARY, BLOB, and TEXT. The collations determine the comparison and sorting of strings. 1.CHAR is suitable for fixed-length strings, VARCHAR is suitable for variable-length strings. 2.BINARY and VARBINARY are used for binary data, and BLOB and TEXT are used for large object data. 3. Sorting rules such as utf8mb4_unicode_ci ignores upper and lower case and is suitable for user names; utf8mb4_bin is case sensitive and is suitable for fields that require precise comparison.

The best MySQLVARCHAR column length selection should be based on data analysis, consider future growth, evaluate performance impacts, and character set requirements. 1) Analyze the data to determine typical lengths; 2) Reserve future expansion space; 3) Pay attention to the impact of large lengths on performance; 4) Consider the impact of character sets on storage. Through these steps, the efficiency and scalability of the database can be optimized.


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