The SQL language is a matter of common knowledge to almost everyone. Even those who do not use it directly in their work have an idea about it. This tool was developed in 1974. Its founding purpose was the storage and processing of information. Today, it is used by almost all database management systems (DB) as a processor to get fast and efficient command processing.
SQL queries are a crucial work component of each web developer and tester. By creating sharp database work, it is used to enhance websites and software. Testing experts can provide entrepreneurs with much data to help them make better decisions. Marketers can use this language to conduct in-depth analyses of their target audience’s behavior.
What fundamental SQL queries should everyone using a DBMS be familiar with? In this article, we’ll concentrate on the types and essential commands that marketers, testers, developers, and other professionals must always be aware of.
Types of SQL queries
The language consists of a specific set of commands and declarative key queries that are not instructions for the database. With the help of such requests, it is possible:
- create, and delete tables from the database;
- enter brand-new and additional information;
- correct existing records;
- seek and find information, considering specific requests.
All key queries can be divided into four main groups. Let’s take a closer look at each of them.
Data Definition Language
It is commonly denoted by the acronym DDL. Among these are the keywords CREATE (creation), RENAME (renaming), DROP, etc. They all imply the design and administration of the database structure. A database is formed using queries, which likewise describe, structure, and pinpoint the precise arrangement of information within it.
Data Manipulation Language or DML
Here, we are talking about the literal manipulation of data. This language is referred to as DML. The category of keywords includes the following commands:
Queries are used to change, retrieve, update, and delete information from the database.
Data Control Language or DCL
It is a data management language, including keywords responsible for permission, rights, and various settings that restrict access to the database. The most popular are DENY and GRANT.
Transaction Control Language or TCL
This abbreviation refers to the language of operations management. Queries in SQL, in this case, are represented by transaction management commands and their life cycles. COMMIT, ROLLBACK TRANSACTION, and BEGIN TRANSACTION are great examples.
Basic SQL commands
CRUPD includes all “Create, Read, UPdate, Delete” activities possible with databases and their data. These are regarded as the primary commands that users can carry out by sending queries straight to the DBMS:
- CREATE – creating information in the database;
- READ – reading, obtaining information from the database;
- UPDATE – updating, performing any manipulations with information;
- DELETE – deletion of data.
You will need to use special keys (operators) to perform various data operations using SQL. Such commands provide the opportunity to work with the DBMS as quickly and efficiently as possible, saving time and obtaining essential data from a large amount of information.
Basic SQL queries can be shown in the following illustrations:
- CREATE DATABASE – making up a database;
- CREATE TABLE – making a new table in the database with the specified column names;
- ALTER TABLE – adding columns to an already developed table;
- INSERT – inserting information into a table and creating new lines;
- SELECT – picking data from the database;
- WHERE – helps to build more specific commands;
- BETWEEN, OR, AND – help to refine the query as much as possible (adding more criteria to WHERE);
- ORDER BY – sorting the output of information by columns, taking into account the specified SELECT command;
- GROUP BY – combining rows with similar data;
- LIMIT – an indication of the highest number of lines that will be displayed in the outcomes;
- UPDATE – updating the record in the database tables;
- DROP COLUMN – remove a column from the table;
- DROP TABLE – delete the entire table.
These are basic SQL queries for beginners, which may be required by absolutely all users working with extensive databases with the help of the structured command language.
Additional functions and subqueries
Programmers, testers, and marketers may require additional commands to perform more specialized database operations. As an illustration, the following aggregate functions let you make calculations inside the created sample:
- COUNT – the command helps to return the number of rows of the received selection if the columns contain a non-NULL value (zero);
- SUM – performs a calculation that returns the sum of the numbers in the specified column;
- AVG – the calculation, the return of the average indicator for the selected column;
- MAX – enables you to return the most significant value;
- MIN – returns the lowest value.
All functions are used with the column name where you need to perform the appropriate action.
There are also nested SQL queries (subqueries). They are commands within other questions that filter the selection values more precisely. For instance, DISTINCT allows you to remove all duplicate results from the returned information.
For many professionals, using structured command language is crucial to their work. We clarified the fundamental keywords that software developers, testers, and marketers would need. SQL queries come in a vast variety. These include circular requests, recursive requests, requests involving different works with variables, and other requests and subqueries.
To cap it all, this basic information is a vital tool for anyone working with a DBMS that stores a lot of data. The ability to swiftly and effectively gather information, analyze it, and make the decisions required for business development is made possible by using SQL queries.