How to Retrieve Data from a Relational DatabaseUsing SQL Introduction The core of data management systems is the relational database model, which has been inuse for many years. A critical component of data management is retrieving data fromrelational 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 therelational data model, is the main topic of this article. The process of retrieving data from arelational data store entails describing how to do so and the internal processing carried outby 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 inthe data management sector. Both traditional distributed big data systems like Spark andcontemporary distributed database management systems like Oracle use SQL in the form ofSpark SQL. Using SQL to Retrieve Data A SELECT-FROM-WHERE clause is a SQL query's most fundamental building block. Thisphrase outlines the attributes that will be output, the logical table that will be used to respondto the query, and the requirement that all required data items must meet. Let's examine asample 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 thatproduce beer are included in the second table, titled beers. The sales table keeps track ofwhich 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 requirementthat the value of the manf attribute equals Heineken in this query. Because Heineken is astring literal and must match exactly in this context, including the case, you'll notice that it isenclosed in quotes. Features of SQL In order to access data from relational databases, SQL offers a wide variety offunctionalities. 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 Heinekenbeers 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, weused the logical table sales and the criteria that the price must be greater than 5 and theattribute 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, andsells.price. Also, we used the logical tables bars and sells, along with the restrictionsthat bars.name's value be equal to sells.bar's and sells.beer's value be equal toHeineken's. Conclusion One of the most basic functions of data management is retrieving data from arelational database. We can effectively get data from relational databases using thepotent tool SQL.