A queue-based database application is an application (or part of one) where multiple users need to work on a pool of records in a queue to process them. The records in the queue are in an “unprocessed” state. After the user works on any record, that record is in a “completed” state and is removed from the queue.
Formulated by a computer scientist at IBM in the 1970s, Query By Example (QBE) is a filtering or search system for databases where there was no need to use a query language.
A database query is a similar action that is most closely associated with some CRUD (create, read, update, delete) function. A database query is a request to access data from a database to manipulate it or retrieve it.
One user needs to select or is assigned to one of the records and works with that data. Any record must never be assigned to more than one user.
What is a database query?
At a very high level, a query is a question. When we talk about queries concerning other people, we expect some answer in return. This is no different for computers when we perform database queries.
A query is a way of requesting information from the database. A database query can be either a select query or an action query. A select query is a query for retrieving data, while an action query requests additional actions to be performed on the data, like deletion, insertion, and updating.
For example, a manager can perform a query to select the hired employees five months ago. The results could be the basis for creating performance evaluations.
This allows us to perform logic with the information we get in response to the query. There are several different approaches to queries, from using query strings to writing with a query language or using a QBE like GraphQL or REST.
With GraphQL, users can query for and receive only the specific data they’re looking for, not more, not less.
A database query is a similar action that is most closely associated with some CRUD (create, read, update, delete) function. A database query is a request to access data from a database to manipulate it or retrieve it.
Query Parameters
Query Parameters are put on the end of a URL as part of a query string. This is how search engines grab search results for parameters a user inputs in a search bar. You can also add query parameters to the end of an endpoint to aid in pagination.
What is Query By Example?
It is done under the hood for you. The timeline for QBE occurred alongside the development of the structured query language (SQL), which we’ll go over in the next section.
More than likely, there is a graphical user interface that a user fills out. Once submitted, the query is built under the hood. This prevents missing input bugs as the query only gets built from the information that it’s given as opposed to a prebuilt query that is expecting specific information.
Let’s look at an example.
Title: Jurassic Park
Director: Steven Spielberg
Year:
Language:
Release:
The resulting SQL that is created:
SELECT * FROM Movies WHERE Title=’Jurassic Park’ AND Director=’Steven Spielberg’;
This is a very basic sampling of the type of QBE form that can be used to generate SQL. Other forms will use drop-downs to add other SQL keywords such as LIKE, CONTAINS, etc.
QBE paved the way for end-user development, allowing those who are not professional software developers or programmers to extend a piece of software to suit their needs. It is currently used in relational and object-oriented databases.
Methods for Creating Queries
Selecting Parameters from a Menu
In this method, the database system displays a list of parameters for you to choose from. This is the simplest way to create a query because there are menus that guide you, but it is also the least flexible.
Query by Example (QBE)
In this method, the system displays a blank record and lets you identify the fields and values that define the query.
This is a method of query creation that authorises the user to look for documents based on an example in the form of a selected text string, or in the form of a document name, or even a list of documents. Because the QBE system develops the actual query, QBE is easier to grasp than formal query languages while still enabling powerful searches.
In terms of database management systems, QBE can be considered a ‘fill-in-the-blanks method of query creation. An example of QBE is the Microsoft Access Query Design Grid. The user inputs criteria into the form to create search conditions for as many fields as desired in order to perform a search. A query is then automatically created to search the database for corresponding data.
Query Language
Many database systems expect you to make requests for information through a stylised query written in a specific query language. This is the most complicated method because it compels you to learn a specific language, but it is also the most flexible.
Query languages are used to create queries in a database.
Languages for database querying
The query language is what allows us actually to take action on databases. It allows us to create, read, update and delete items on our database, as well as more advanced queries like filtering and counting.
Structured Query Language (SQL) is the most famous of the query languages. SQL grew up alongside the Query By Example (QBE) system developed by IBM in the 1970s. It serves the basis of relational databases.
With SQL, we can store, retrieve, and manipulate data using simple code snippets, called queries, in an RDBMS (relational database management system).
The data is stored in the RDBMS in a structured way, where there are relations between the different entities and variables in the data.
These relations are defined by the database schema, which specifies the relationship between various entities and the organization of data for the entities.
Examples of Query Languages
Microsoft Structured Query Language (SQL) is the ideal query language. Other expansions of the language under the SQL query umbrella include:
MySQL
Oracle SQL
NuoDB
Query languages for other types of databases, such as NoSQL databases and graph databases, include the following:
Cassandra Query Language (CQL)
Neo4j’s Cypher
Data Mining Extensions (DMX)
XQuery
Using available parameters
The software, by default, has lists of parameters on its menu. Users can choose one, and the system will then guide you to produce the desired output. It’s easy but not flexible and offers limited operations.
Advantages
● The database has the possibility to uncover intricate movements and actions, but this power is only utilised through the use of the query. A complex database contains multiple tables storing countless amounts of data. A query lets you filter it into a single table so that you can analyse it much more easily.
● Queries also can execute calculations on your data, summarise your data for you, and even automate data management tasks. You can also evaluate updates to your data prior to committing them to the database for still more versatility of usage.
● Queries can perform a number of various tasks. Mainly, queries are used to search through data by filtering specific criteria. Other queries contain append, crosstab, delete, make a table, parameter, totals, and update tools, each of which performs a specific function. For example, a parameter query executes the distinctions of a specific query, which triggers a user to enter a field value, and then it makes use of that value to make the criteria. In comparison, totals queries let users organise and summarise data.
● In a relational database, which is composed of records or rows of data, the SQL SELECT statement query lets the user select data and deliver it to an application from the database. The resulting query is saved in a result-table, which is referred to as the result-set. The SELECT statement can be divided into other specific statements, like FROM, ORDER BY and WHERE. The SQL SELECT query can also group and combine data, which could be useful for creating analyses or summaries.
So finally, if you have thousands of data rows. Manipulating them doesn’t have to be hard. Besides, most query languages are intuitive, meaning that they are easy to learn once you understand some basic rules. There is still a lot to learn when it comes to databases and querying. Let’s get our hands dirty with database queries and deal with our data like pros.