What is a Database Query?
A database query is essentially a request to access data from a database for the purpose of manipulating it or retrieving it. It is a type of action that is most closely associated with some sort of CRUD (create, read, update, delete) function. The request comes in a database table or a combination of tables using a code known as the query language. This makes it possible for the system to understand and process the query.
Database queries enable you to perform logic with the information we get in response to the query. There are various approaches to database queries - all the way from using query strings, to writing with a query language or using a QBE like GraphQL or REST.
When they use GraphQL, users can query for and receive only the specific data they’re looking for; nothing more, nothing less. It makes it possible for you to request specific data, thus offering clients more control over what information is sent. This becomes a bit tougher with the alternative architecture, REST, due to the fact that the backend defines what data is available for each resource on a URL.
What is the Purpose of a Database Query?
The purpose of a query is to enable you to find your data and perform operations on it. If your database is designed well, the data that you want to present through a form or report will tend to be located in multiple tables. You can use a query to retrieve the information from various tables and assemble it for display in the form or report.
The query will be a request for data results from your database or for action on the data, or even for both. The query can provide you with answers to simple questions, carry out calculations, combine data from different tables, add, change, or delete data from a database. Due to the fact that queries are so versatile, there are several types of queries and you would create a type of query based on the task.
What are the Types of Query in Database?
There are many types of queries with varying uses. Here are the two major types of queries in a database:
Select query
The point of a select query is to retrieve data from a table or perform calculations.
Action query
An action query is used for the purpose of adding, changing or deleting data. There are specific types of action queries for every task.
What are Common Queries?
Here are some of the most common queries:
- SELECT – this query retrieves data from the database. It’s one of the most popular commands, since every request begins with a select query.
- AND – this query combines data from one or multiple tables.
- CREATE TABLE – this query creates different tables and specifies the name of each column within.
- ORDER BY – this query sorts data results either in numerical or alphabetical order.
- SUM – this query summarizes the data from a particular column.
- UPDATE – this query modifies the existing rows in a table.
- INSERT – this query is used to add new data or rows to an existing table.
- WHERE – this query is used to filter data and get its value on the basis of a set condition.
You could even get some variations by combining some of the commands that are listed above. As an example, you could use the SELECT query along with other commands like AND or SUM in order to aggregate data or combine results.
What is Query By Example?
Query By Example (QBE) is a filtering or search system for databases where there is no need for making use of a query language. It was formulated by a computer scientist at IBM in the 1970s, and the system does everything for you instead of making you use a querying language.
Query By Example was created around the same time when the structured query language (SQL) was being developed.
Quite often, there will be a graphical user interface that a user fills out. After the submission, the query will be built by the system itself under the hood. This helps it avoid missing input bugs as the query only gets built from the information that it is provided with instead of making use of a prebuilt query that is expecting specific information.
QBE paved the way for end-user development, enabling people who do not happen to be professional software developers or programmers to extend a piece of software so that it suits their needs. It is currently used in relational and some object-oriented databases.
What are the types of Query Languages?
The query language is what makes it possible for you to actually take action on databases. It enables you to create, read, update and delete items on your database, and even perform more advanced queries such as filtering and counting.
Structured Query Language (SQL) is the most popular of the query languages. It acts as the basis of relational databases. It enables you to 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 manner, in which there are relations that exist between the different entities and variables in the data.
SQL databases are relational and make use of predefined schemas that need you to specify your data structure.
There is yet another type of query language called NoSQL (Not Only Structured Query Language). The data structure is the main difference between these query languages.
NoSQL databases are non-relational and make use of dynamic schemas for unstructured data.
SQL and NoSQL both have their own applications. An SQL database is good for an ACID-compliant data structure, while a NoSQL database could be better for unstructured documents, key-values, or graphs.
