The logical structure of Oracle database focuses on how data is organized by users and developers, including tables, views, patterns and table spaces; the physical structure involves the actual storage of data on disk, including data files, redo logs, control files, etc. 1. The logical structure includes tables, views, indexes, patterns and table spaces, which determine how users access data; 2. The physical structure consists of data files, redo logs, control files and archive logs, which are responsible for the persistence and recovery of data; 3. The table space is a key bridge connecting logic and physics, and its capacity is limited by the underlying data files; 4. Different roles have different levels of attention, developers focus on logic optimization, and DBA pays more attention to physical management; 5. Understanding the differences between the two can help efficiently troubleshoot problems, optimize performance and reasonable management

PL/SQLextendsSQLwithproceduralfeaturesbyaddingvariables,controlstructures,errorhandling,andmodularcode.1.Itallowsdeveloperstowritecomplexlogiclikeloopsandconditionalswithinthedatabase.2.PL/SQLenablesthedeclarationofvariablesandconstantsforstoringinte

AutomaticStorageManagement(ASM)isOracle’sbuilt-instoragesolutiondesignedtosimplifyandoptimizethemanagementofdatabasestorage.1.IteliminatestheneedforexternalvolumemanagersorRAIDconfigurations.2.ASMautomaticallybalancesI/Oacrossdisks,preventinghotspots

OracleDataGuard supports three standby databases: physical, logical, and snapshot. 1. The physical standby database is a byte-level copy of the main library, synchronized using RedoApply, suitable for disaster recovery; 2. The logical standby database applies changes through SQLApply, which can be structured different from the main library, suitable for reporting and selective replication; 3. The snapshot standby database is based on physical standby and can be converted into a writable state for testing, and FlashbackDatabase needs to be enabled. Select according to requirements: requires data consistency and quick switching of physics, requires flexibility and support for report selection logic, and select snapshots if you need to test the production environment copy.

InPL/SQL,exceptionsarecategorizedintotwotypes:predefinedanduser-defined.1.Predefinedexceptionsarebuilt-inerrorssuchasNO_DATA_FOUND,TOO_MANY_ROWS,VALUE_ERROR,ZERO_DIVIDE,andINVALID_NUMBER,whichareautomaticallyraisedduringspecificruntimeerrors.2.User-d

SubqueriesinOracleSQL—scalar,multi-row,andcorrelated—enhancequeryflexibilitybyenablingmodularlogic,dynamicdatahandling,andcomplexfiltering.Scalarsubqueriesreturnasinglevalueandareidealforcomparisonsorexpressionssuchascomputingtheaveragesalary;1.theys

Oracle sequences are independent database objects used to generate unique values ??across sessions and transactions, often used for primary keys or unique identifiers. Its core mechanism is to generate a unique value through NEXTVAL increment, and CURRVAL obtains the current value without incrementing. Sequences do not depend on tables or columns, and support custom start values, step sizes and loop behaviors. Common scenarios during use include: 1. Primary key generation; 2. Order number; 3. Batch task ID; 4. Temporary unique ID. Notes include: transaction rollback causes gaps, cache size affects availability, naming specifications and permission control. Compared to UUID or identity columns, sequences are suitable for high concurrency environments, but they need to be traded down based on the needs.

In Oracle, the schema is closely associated with the user account. When creating a user, the same-name mode will be automatically created and all database objects in that mode are owned. 1. When creating a user such as CREATEUSERjohn, create a schema named john at the same time; 2. The tables created by the user belong to their schema by default, such as john.employees; 3. Other users need authorization to access objects in other schemas, such as GRANTSELECTONsarah.departmentsTOjohn; 4. The schema provides logical separation, used to organize data from different departments or application modules.