What is a Database Query ?
A database query allows you to ask a specific data-related question based on a pre-defined code. A database management system (DBMS) is created to define a data query with the system sourcing an answer direct from the database before retrieving and presenting it.
What is a query in a database?
Enterprise generates and manages huge volumes of data, whether in value or word form. These data sets are typically stored in a database in tables containing columns and rows, which contain the individual data, its attributes and records of information. However, related data is typically distributed across different locations within the database. To efficiently recover this dispersed data, the system must strategically define database queries, ensuring the use of a targeted approach to information retrieval.
So what is a query in a database and why is it so important? Database queries are powerful. They allow you to query data on the database with the DBMS then pulling out and compiling data results based on your data query. Any results are delivered back to you for analysis. Those are the basics but database queries actually offer you far more functionality and capabilities.
Knowing how to define and design a query is essential to efficiently source and retrieve these related data sets. Undertaking this database query process manually would be a logistical nightmare if done manually, requiring a ‘needle in a haystack’ approach – or in most cases, potentially a massive number of needles.
For instance, database queries can summarise, adjust and update data, and even automate data management tasks, for example an accounts statement or a Microsoft spreadsheet. Combined, a data query allows organisations to glean crucial insights on every aspect of their enterprise, from, say, salary levels across departments and employee performance through to marketing campaign success rates and customer behaviours and demographics, encompassing a number of valuable perspectives.
What are the 2 main types of database queries?
There are two principal types of database query – the action query and the select query – or combinations of both. Each type of query is a powerful subset of queries that help you to alter or interrogate any records contained in the database:
How to define a query: Action database queries
Action database queries allow you to define queries that carry out a selection of modification activities on the database and its tables and columns and rows, right down to individual record level. For instance:
- Add a new data table into a database using a Make-Table data query
- Add a new row or record to a database table with an Insert data query
- Alter existing records within a database table with an Update data query
- Take out a record from a database table using a Delete data query
- Remove an entire table from a database with a Drop Table data query
- Generate an index with a Create Index data query.
These methods to design and define queries combined with other action queries enable you to carry out data management tasks quickly and efficiently using drop tables and insert mode, helping to keep data updated and accurate by protecting data integrity. Note: such powerful data query design methods must also only be used by personnel who are aware of the risk of action database queries and their ability to make significant changes to data assets. This highlights the need to define a query with precision. It’s also why having data backup[LINK] and business continuity[LINK] strategies is vital in case any errors are made.
3 examples of an action database query
The following three data query examples are written in SQL for relational databases:
Insert query
The following data query adds a new employee record column or row with full details on the employee including name, department and salary:
INSERT INTO Employees (EmployeeID, FirstName, LastName, Department, Salary)
VALUES (101, ‘John’, ‘Smith’, ‘Human Resources’, 60000);
Update query
The following data query adds a 10% salary increase column or row for all employees working in marketing:
UPDATE Employees
SET Salary = Salary * 1.10
WHERE Department = 'Marketing';
Delete query
The following example of a data query is a way to delete customer records stored in the customer's table based on when they last made a purchase. This is used to create a mode to cull inactive customers from the database:
DELETE FROM Customers
WHERE LastPurchaseDate < '2022-06-06';
How to define a query: Select database queries
Select database queries enables you to define queries that retrieve data for investigation and analysis. Like action queries, select queries offer several useful capabilities for extrapolating data sets. For instance:
- Make results easier to read and understand with Cross-tab database queries
- Take data from different tables and combine them with Join database queries
- Source summary values including averages with Aggregate database queries
- Take results sourced from several select queries and create a single data set with Union database queries.
When considering how to define queries, a special mention should be given to parameter queries, which allow you to query database by setting up database query criteria to filter your searches. These enable you to extract targeted data sets from your database. The parameters of the query database can be changed as and when required, offering a flexible solution for identifying and extracting key information from across potentially huge volumes of data in moments.
Ultimately, select-related database queries are designed to give you access to information that can help identify trends, reveal performance or productivity bottlenecks, and deliver the intel you need for the execution of smarter, more informed business decisions. And in an era where data volumes continue to explode, functionality like this is more vital than ever.
3 examples of a select database query
Join database queries
The following query example is a straightforward method of retrieving employee names and ‘joining’ these names with the departments they work in:
SELECT Employees.EmployeeID, Employees.FirstName, Employees.LastName, Departments.DepartmentName
FROM Employees
INNER JOIN Departments ON Employees.DepartmentID = Departments.DepartmentID;
Cross-tab database queries
The following data query deploys a cross-tab format to offer a summary of sales quantities for each product by month. It achieves this by making a request for data from the orders table column or row based on the order data, presenting the results in table form:
SELECT ProductID,
SUM(CASE WHEN Month(OrderDate) = 1 THEN Quantity ELSE 0 END) AS Jan,
SUM(CASE WHEN Month(OrderDate) = 2 THEN Quantity ELSE 0 END) AS Feb,
-- ... Repeat for other months
SUM(Quantity) AS Total
FROM Orders
GROUP BY ProductID;
Parameter database queries
The following method to define a query sets up a parameter that can identify and retrieve an order from an individual customer:
SELECT OrderID, OrderDate, TotalAmount
FROM Orders
WHERE CustomerID = ?; -- Parameter placeholder
What is a database query language?
It’s important to note that you can’t simply make up a unique type of data query and request it. Instead, your database query must ‘speak’ to the database in a language it understands so any data queries can be processed. This is done using predefined code, which is known as a query language. Several different languages can be deployed to define a query, giving you the ability to take full control of the execution of your database:
Types of relational database query languages
These are specific languages that work with relational databases (databases that store related data points in accessible form). A popular example is Microsoft’s Structured Query Language (SQL) to define queries with other options in this group including MySQL, Oracle SQL and NuoDB.
For enterprises with no experience in data query language and execution, a potential stopgap is to use Query by example. This enables you to perform simple queries using the software solution’s popular user filters, which feature search variables that you fill in before launching. While useful, QBE is not a replacement for an SQL database query system.
Types of non-relational database query languages
Languages are also available for non-relational databases, known as NoSQL databases. Unlike relational variants, these do not deploy tables, instead using the execution of other formats including documents and key values. Database query languages for non-relational databases include Cassandra Query Language (CQL), XQuery and Data Mining Extensions (DMX).
How to perform a database query
You typically use a database management system (DBMS) to perform the execution of queries on relational databases. While specific database queries require different actions, what follows is the most common type of process to define a query and request data:
Select a DBMS
There are several different DBMS solutions available including MySQL, Oracle and others. Each feature their own database query tools as well as specific syntax.
Get started
Use your DBMS’s interface to define your query and execute it. It’s crucial that you have a full understanding of SQL so you can construct queries that the DBMS can actually understand.
Create the database query
It’s essential to note that there are two main data query types – action and select. Within these are powerful query types that help you perform actions such as updating, adding or deleting data, or are select-based such as retrieving data sets based on your customised criteria. Once created, simply run the database query.
View results
The Select query is answered with results shown by the DMBS onscreen, usually in a data table. If there are issues when you define a data query, the DBMS will present you with error messages that you can use to rectify any search so it can be resubmitted.
Future proof searches
To help reduce the busy work of creating the same queries time and again, most DBMSs let you save database queries so the data query can be selected quickly and its execution deployed again.
What is a database query language?
It’s important to note that you can’t simply make up a unique type of data query and request it. Instead, your database query must ‘speak’ to the database in a language it understands so any data queries can be processed. This is done using predefined code, which is known as a query language. Several different languages can be deployed to define a query, giving you the ability to take full control of the execution of your database:
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