欢迎进入C/C++编程社区论坛,与200万技术人员互动交流 >>进入 void smsLogon::InitSQLServer(CString server, CString db, CString UserName, CString Pwd) { m_pConnection.CreateInstance("ADODB.Connection"); CString strCn; strCn.Empty(); strCn="prov
欢迎进入C/C++编程社区论坛,与200万技术人员互动交流 >>进入
void smsLogon::InitSQLServer(CString server, CString db, CString UserName, CString Pwd)
{
m_pConnection.CreateInstance("ADODB.Connection");
CString strCn;
strCn.Empty();
strCn="provider=SQLOLEDB;data source="+server
+";initial catalog="+db
+";userID="+UserName
+";PassWord="+Pwd;
_variant_t bcnstr=_variant_t(strCn);
_variant_t bunstr=_variant_t(UserName);
_variant_t bpwdstr=_variant_t(Pwd);
//打开一个连接
try
{
m_pConnection->Open(_bstr_t(bcnstr),_bstr_t(bunstr),
_bstr_t(bpwdstr),-1);//adOpenUnspecified
}
catch(_com_error e)
{
CString errormessage;
errormessage.Format("Warning: 连接数据库发生异常. 错误信息: %s; 文件: %s; 行: %d\n", e.ErrorMessage(), __FILE__, __LINE__);
AfxMessageBox(errormessage);
}
catch(...)
{
AfxMessageBox("Warning :连接数据库时发生未知错误");
}
}
void smsLogon::ExitDB() //退出时关闭数据库连接
{
if(m_pConnection!=NULL)
{
m_pConnection->Close();//关闭连接
m_pConnection.Release();//释放对象
}
}

MySQLstringtypesimpactstorageandperformanceasfollows:1)CHARisfixed-length,alwaysusingthesamestoragespace,whichcanbefasterbutlessspace-efficient.2)VARCHARisvariable-length,morespace-efficientbutpotentiallyslower.3)TEXTisforlargetext,storedoutsiderows,

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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