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Database Articles
Page 130 of 547
How to select last 10 rows from MySQL?
To select last 10 rows from MySQL, we can use a subquery with SELECT statement and Limit concept. The following is an example. Creating a table. mysql> create table Last10RecordsDemo -> ( -> id int, -> name varchar(100) -> ); Query OK, 0 rows affected (0.75 sec) Inserting records into the table. mysql> insert into Last10RecordsDemo values(1, 'John'), (2, 'Carol'), (3, 'Bob'), (4, 'Sam'), (5, 'David'), (6, 'Taylor'); Query OK, 6 rows affected (0.12 sec) Records: 6 Duplicates: 0 Warnings: 0 mysql> insert into Last10RecordsDemo ...
Read MoreWhat are the applications of DBMS?
The Database Management System (DBMS) is defined as a software system that allows the user to define, create and maintain the database and provide control access to the data.It is a collection of programs used for managing data and simultaneously it supports different types of users to create, manage, retrieve, update and store information.Applications of DBMSIn so many fields, we will use a database management system.Let’s see some of the applications where database management system uses −Railway Reservation System − The railway reservation system database plays a very important role by keeping record of ticket booking, train’s departure time and ...
Read MoreWhat are the DCL commands in DBMS?
Data control language (DCL) is used to access the stored data. It is mainly used for revoke and to grant the user the required access to a database. In the database, this language does not have the feature of rollback.It is a part of the structured query language (SQL).It helps in controlling access to information stored in a database. It complements the data manipulation language (DML) and the data definition language (DDL).It is the simplest among three commands.It provides the administrators, to remove and set database permissions to desired users as needed.These commands are employed to grant, remove and deny ...
Read MoreWhat is Query Optimization?
Query optimization is of great importance for the performance of a relational database, especially for the execution of complex SQL statements. A query optimizer decides the best methods for implementing each query.The query optimizer selects, for instance, whether or not to use indexes for a given query, and which join methods to use when joining multiple tables. These decisions have a tremendous effect on SQL performance, and query optimization is a key technology for every application, from operational Systems to data warehouse and analytical systems to content management systems.There is the various principle of Query Optimization are as follows −Understand ...
Read MoreThe concept of indexing in Apache Cassandra
Indexing in Apache Cassandra is a way to improve the efficiency and performance of queries on non-primary key columns. In Cassandra, data is organized in tables and each table has a primary key, which consists of one or more columns that uniquely identify each row in the table. Queries that use the primary key to retrieve data are very efficient, but queries that use other columns in the WHERE clause can be slower. Cassandra has secondary indexes that enable querying on columns other than the main key columns to solve this problem. A secondary index is built on a table's ...
Read MoreConfiguring Clusters in Cassandra
Cassandra is a NoSQL database that is made to manage massive volumes of data over several nodes and is extremely scalable. Data distribution over numerous nodes in a cluster, which enables high availability and fault tolerance, is one of Cassandra's core characteristics. In this post, we'll go through the syntax and examples for configuring Cassandra clusters. Configuring a Cassandra Cluster Let's first talk about the fundamental structure of a Cassandra cluster before getting into the specifics of constructing one. Many nodes, each of which can either be a seed node or a normal node, make up a Cassandra cluster. The ...
Read MoreConditionally Updating Columns
In conclusion, creating a Cassandra cluster entails selecting the seed nodes, setting the replication factor, configuring the IP addresses and ports for each cluster node, as well as additional configuration options like the cluster name. The main configuration file for Cassandra clusters is the cassandra.yaml file. Cassandra clusters may offer high availability and fault tolerance for massive volumes of data with the proper configuration. You may effectively configure a Cassandra cluster to suit your unique requirements by adhering to the syntax and examples shown in this article. Syntax UPDATE table_name SET column1 = value1, column2 = value2, ... WHERE condition; ...
Read MoreCondition of schedules to View-equivalent
View-equivalence is a term used in database management systems to describe the circumstance in which two schedules, when applied to the same database, yield the same result set. This requirement is necessary to guarantee data correctness and consistency in database applications. There are requirements that schedules must meet in order to achieve view equality. These circumstances are − Conflict Serializability − The conflicting operations in a schedule must be performed in the same sequence for it to be conflict serializable. Operations that access the same data item and at least one of which affects the data are said to ...
Read MoreConcept of Time in database
In the form of a relation, a database is used to mimic the status of some part of the real world outside. Database systems, in general, store just one state, which is the present state of the actual world, and do not keep data regarding prior and past states, except sometimes as audit trails. If the real world's current state changes, the database is edited and updated, and knowledge about the previous state is lost. But, in the majority of real-world applications, it is important to store and retrieve information about previous states. A student database, for example, must have ...
Read MoreComputer-based control in Database
This article will provide a broad review of computer-based controls before moving into the computer-based controls in databases available in a multi-user database system. Let's discuss all of them one by one. A group of security procedures called computer-based controls are used in DBMSs to safeguard the database against illegal access, alteration, or destruction. These safeguards are intended to guarantee that the database can only be accessed by authorized users and that the data is safe from accidental or deliberate destruction. Physical controls and administrative processes are only a couple of the several remedies available to deal with threats to ...
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