What is Oracle Application Express (APEX), and how can it be used for rapid web application development?

TheWITHclauseinOracle,alsoknownassubqueryfactoring,enablesdefiningcommontableexpressions(CTEs)forimprovedqueryreadabilityandperformance.1.ThebasicsyntaxusesWITHcte_nameAS(SELECT...)followedbyamainqueryreferencingtheCTE.2.AsingleCTEexamplecomputesaver

Aviewdoesnotstoredataphysicallyandexecutestheunderlyingqueryeachtimeitisaccessed,whileamaterializedviewstoresthequeryresultasaphysicaltable.2.Materializedviewsgenerallyofferfasterqueryperformancebecausetheyaccessprecomputeddata,whereasviewscanbeslowe

First, confirm whether the listener on the database server has been started, use lsnrctlstatus to check, if it is not running, execute lsnrctlstart to start; 2. Check whether the HOST and PORT settings in the listener.ora configuration file are correct, avoid using localhost, and restart the listener after modification; 3. Use the netstat or lsof command to verify whether the listener is listening on the specified port (such as 1521). The client can test port connectivity through telnet or nc; 4. Ensure that the server and network firewall allow the listening port communication, the Linux system needs to be configured with firewalld or iptables, and Windows needs to enable inbound

Usejdbc:oracle:thin:@hostname:port:sidforSID-basedconnections,e.g.,jdbc:oracle:thin:@localhost:1521:ORCL.2.Usejdbc:oracle:thin:@//hostname:port/service_nameforservicenames,requiredforOracle12c multitenant,e.g.,jdbc:oracle:thin:@//localhost:1521/XEPDB

Use the CREATESEQUENCE statement to create sequences, which are used to generate unique values, often used for primary or proxy keys; 2. Common options include STARTWITH, INCREMENTBY, MAXVALUE/MINVALUE, CYCLE/NOCYCLE and CACHE/NOCACHE; 3. Get the next value through NEXTVAL, and CURRVAL gets the current value; 4. You can use sequence values to insert data in the INSERT statement; 5. It is recommended to avoid cache to prevent the loss of values due to crashes, and the sequence values will not be released due to transaction rollback; 6. Use DROPSEQUENCE to delete sequences when no longer needed.

When encountering an ORA-01017 error, it means that the login is denied. The main reason is that the user name or password is wrong or the account status is abnormal. 1. First, manually check the user name and password, and note that the upper and lower case and special characters must be wrapped in double quotes; 2. Confirm that the connected service name or SID is correct, and you can connect through tnsping test; 3. Check whether the account is locked or the password expires, and the DBA needs to query the dba_users view to confirm the status; 4. If the account is locked or expired, you need to execute the ALTERUSER command to unlock and reset the password; 5. Note that Oracle11g and above versions are case-sensitive by default, and you need to ensure that the input is accurate. 6. When logging in to special users such as SYS, you should use the assysdba method to ensure the password.

To find the second highest salary in Oracle, the most commonly used methods are: 1. Use ROW_NUMBER() or RANK(), where ROW_NUMBER() assigns a unique sequence number to each row, which is suitable for obtaining the second row of data. RANK() will skip subsequent rankings when processing parallelism; 2. Use MAX() and subqueries to pass SELECTMAX(salary)FROMemployeesWHEREsalary

Ensure that the system meets prerequisites such as hardware, operating system and swap space; 2. Install the required software packages, create oracle users and groups, configure kernel parameters and shell restrictions; 3. Download and decompress the Oracle database software to the specified directory; 4. Run runInstaller as oracle user to start graphical or silent installation, select the installation type and execute the root script; 5. Use DBCA to create the database silently and set the instance parameters; 6. Configure ORACLE_BASE, ORACLE_HOME, ORACLE_SID and PATH environment variables; 7. Start the instance through sqlplus/assysdba and verify the database status, confirm that the installation is successful,