How to Retrieve Data from a Relational Database

How to Retrieve Data from a Relational Database Using SQL Introduction The core of data management systems is the relational database model, which has been in use for many years. A critical component of data management is retrieving data from relational databases, and this article describes how to do it using SQL. Understanding Data Retrieval The process of identifying and obtaining data from a data source is known as data retrieval. Data retrieval from a relational data store that adheres to a certain data model, such as the relational data model, is the main topic of this article. The process of retrieving data from a relational data store entails describing how to do so and the internal processing carried out by the data management system to compute or assess the stated retrieval request. Structured Query Language (SQL) The preferred query language for relational databases is SQL (Structured Query Language). SQL's capacity to handle and retrieve structured data has led to its widespread adoption in the data management sector. Both traditional distributed big data systems like Spark and contemporary distributed database management systems like Oracle use SQL in the form of Spark SQL. Using SQL to Retrieve Data A SELECT-FROM-WHERE clause is a SQL query's most fundamental building block. This phrase outlines the attributes that will be output, the logical table that will be used to respond to the query, and the requirement that all required data items must meet. Let's examine a sample search.. Example Query Let's say we have a business schema with three relations or tables. The names, locations, and license numbers of the bars are listed in the first table. The names and companies that produce beer are included in the second table, titled beers. The sales table keeps track of which establishment and at what price sells which beer. We may use the SQL query below to get the names of the beers that Heineken produces: SELECT name FROM beers WHERE manf = 'Heineken'; We defined the output attribute name, the logical table to use as beers, and the requirement that the value of the manf attribute equals Heineken in this query. Because Heineken is a string literal and must match exactly in this context, including the case, you'll notice that it is enclosed in quotes. Features of SQL In order to access data from relational databases, SQL offers a wide variety of functionalities. Here are some other SQL examples that highlight some of these features: ● Example Query 2 We may use the following SQL query to retrieve the names and manufacturers of Heineken beers that cost more than $5: SELECT name, manf, price FROM sells WHERE manf = 'Heineken' AND price > 5; Name, manf, and price were the output attributes that were supplied in this query. Also, we used the logical table sales and the criteria that the price must be greater than 5 and the attribute manf's value must equal Heineken. ● Example Query 3 We may use the following SQL query to locate the bars that serve Heineken beer: SELECT bars.name, bars.address, sells.price FROM bars, sells WHERE bars.name = sells.bar AND sells.beer = 'Heineken'; The output characteristics for this query were bars.name, bars.address, and sells.price. Also, we used the logical tables bars and sells, along with the restrictions that bars.name's value be equal to sells.bar's and sells.beer's value be equal to Heineken's. Conclusion One of the most basic functions of data management is retrieving data from a relational database. We can effectively get data from relational databases using the potent tool SQL.