Top 50 Rdbms Interview Questions You Must Prepare 16.Aug.2022

An entity set may not have sufficient attributes to form a primary key, and its primary key compromises of its partial key and primary key of its parent entity, then it is said to be Weak Entity set.

The database and DBMS software together is called as Database system.

The domain of attribute must include only atomic (simple, indivisible) values.

Along with the RDBMS software, Oracle provides two utilities that you can use to back up and restore the database. These utilities are Export and Import.
The Export utility dumps the definitions and data for the specified part of the database to an operating system binary file. The Import utility reads the file produced by an export, recreates the definitions of objects, and inserts the data.
If Export and Import are used as a means of backing up and recovering the database, all the changes made to the database cannot be recovered since the export was performed. The best you can do is recover the database to the time when the export was last performed.

It is an applied predicate calculus specifically tailored for relational databases proposed by E.F. Codd.
E.g. of languages based on it are DSL ALPHA, QUEL.

It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.

It is a program module, which is responsible for fetching data from disk storage into main memory and deciding what data to be cache in memory.

Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties

  •  t3[x] = t4[X] = t1[X] = t2[X]
  •  t3[Y] = t1[Y] and t4[Y] = t2[Y]
  •  t3[Z] = t2[Z] and t4[Z] = t1[Z]

where [Z = (R-(X U Y)) ]

Oracle "formats" the database files into a number of Oracle blocks when they are first created—making it easier for the RDBMS software to manage the files and easier to read data into the memory areas.
The block size should be a multiple of the operating system block size. Regardless of the block size, the entire block is not available for holding data; Oracle takes up some space to manage the contents of the block. This block header has a minimum size, but it can grow.
These Oracle blocks are the smallest unit of storage. Increasing the Oracle block size can improve performance, but it should be done only when the database is first created.
Each Oracle block is numbered sequentially for each database file starting at @Two blocks can have the same block address if they are in different database files.

It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.

There are three levels of abstraction:

  •  Physical level: The lowest level of abstraction describes how data are stored.
  •  Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
  •  View level: The highest level of abstraction describes only part of entire database.

There are two Integrity rules.

  •  Entity Integrity: States that “Primary key cannot have NULL value”.
  •  Referential Integrity: States that “Foreign Key can be either a NULL value or should be Primary Key value of other relation.

It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.

It is a program module, which manages the allocation of space on disk storage and data structure used to represent information stored on a disk.

It specifies user views and their mappings to the conceptual schema.

Data independence means that “the application is independent of the storage structure and access strategy of data”. In other words, The ability to modify the schema definition in one level should not affect the schema definition in the next higher level.
Two types of Data Independence:

  •  Physical Data Independence: Modification in physical level should not affect the logical level.
  •  Logical Data Independence: Modification in logical level should affect the view level.

The High level or Non-procedural DML can specify and retrieve many records in a single DML statement. This retrieve of a record is said to be Set-at-a-time or Set-oriented.

A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashes.

Join Dependency:

A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.

Inclusion Dependency:

An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.

Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database
You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures.

  •  Redundancy is controlled.
  •  Unauthorised access is restricted.
  •  Providing multiple user interfaces.
  •  Enforcing integrity constraints.
  •  Providing backup and recovery.

A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.

Extension : It is the number of tuples present in a table at any instance. This is time dependent.

Intension : It is a constant value that gives the name, structure of table and the constraints laid on it.

Procedures that are not part of a package are known as stand-alone because they independently defined. A good example of a stand-alone procedure is one written in a SQL*Forms application. These types of procedures are not available for reference from other Oracle tools. Another limitation of stand-alone procedures is that they are compiled at run time, which slows execution.

It is procedural query language. It consists of a set of operations that take one or two relations as input and produce a new relation.

It executes low-level instruction generated by compiler.

The Oracle system processes, also known as Oracle background processes, provide functions for the user processes—functions that would otherwise be done by the user processes themselves Oracle database-wide system memory is known as the SGA, the system global area or shared global area. The data and control structures in the SGA are shareable, and all the Oracle background processes and user processes can use them.
The combination of the SGA and the Oracle background processes is known as an Oracle instance.

A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.

It is the program module, which tests for the satisfaction of integrity constraint and checks the authority of user to access data.

It is a collection of all entities of particular entity type in the database.

PL/SQL uses cursors for all database information accesses statements. The language supports the use two types of cursors.

  •  Implicit
  •  Explicit

This language is to specify the internal schema. This language may specify the mapping between two schemas.

Different phases are

  •  Analysis phase
  •  Redo Phase
  •  Undo phase

A data base schema is specifies by a set of definitions expressed by a special language called DDL.

A collection of conceptual tools for describing data, data relationships data semantics and constraints.

A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.

A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true

  •  X is subset or equal to (or) XY = R.
  •  X is a super key.

It is a program module, which ensures that database, remains in a consistent state despite system failures and concurrent transaction execution proceeds without conflicting.

No.
PRODUCT: Concatenation of every row in one relation with every row in another.
JOIN: Concatenation of rows from one relation and related rows from another.

A view may be thought of as a virtual table, that is, a table that does not really exist in its own right but is instead derived from one or more underlying base table. In other words, there is no stored file that direct represents the view instead a definition of view is stored in data dictionary. Growth and restructuring of base tables is not reflected in views. Thus the view can insulate users from the effects of restructuring and growth in the database. Hence accounts for logical data independence.

A relation Schema denoted by R(A1, A2, …, An) is made up of the relation name R and the list of attributes Ai that it contains.

A relation is defined as a set of tuples. Let r be the relation which contains set tuples (t1, t2, t3, ..., tn). Each tuple is an ordered list of n-values t=(v1,v2, ..., vn).

The collection (or set) of similar relationships.

I/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management.

It is one, which keeps its Physical Structure hidden from user.

determines an optimal access path to store or retrieve the data.

The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.

A database is a logically coherent collection of data with some inherent meaning, representing some aspect of real world and which is designed, built and populated with data for a specific purpose.

A Functional dependency is denoted by X Y between two sets of attributes X and Y that are subsets of R specifies a constraint on the possible tuple that can form a relation state r of R. The constraint is for any two tuples t1 and t2 in r if t1[X] = t2[X] then they have t1[Y] = t2[Y]. This means the value of X component of a tuple uniquely determines the value of component Y.

The tuple-oriented calculus uses a tuple variables i.e., variable whose only permitted values are tuples of that relation. E.g. QUEL
The domain-oriented calculus has domain variables i.e., variables that range over the underlying domains instead of over relation. E.g. ILL, DEDUCE.