SQL Course
A programming language called structured query language (SQL) is used to store and process data in relational databases. Information is stored in tabular form in relational databases, where distinct data properties and the numerous relationships between the data values are represented by rows and columns. Information can be stored, updated, removed, searched for, and retrieved from databases using SQL commands. SQL can also be used to optimize and maintain database performance
SQL table
The fundamental component of a relational database is a SQL table. The SQL database table is made up of columns and rows. To maximize data storage capacity, database engineers establish links between various database tables.
For example, the database engineer creates a SQL table for products in a store:
| Product ID | Product Name | Color ID |
| 0001 | Mattress | Color 1 |
| 0002 | Pillow | Color 2 |
Then the database engineer links the product table to the color table with the Color ID:
| Color ID | Color Name |
| Color 1 | Blue |
| Color 2 | Red |
SQL statements
SQL statements, or SQL queries, are valid instructions that relational database management systems understand. Software developers build SQL statements by using different SQL language elements. SQL language elements are components such as identifiers, variables, and search conditions that form a correct SQL statement.
For example, the following SQL statement uses a SQL INSERT command to store Mattress Brand A, priced $499, into a table named Mattress_table, with column names brand_name and cost:
INSERT INTO Mattress_table (brand_name, cost)
VALUES(‘A’,’499’);
Stored procedures
Stored procedures are a collection of one or more SQL statements stored in the relational database. Software developers use stored procedures to improve efficiency and performance. For example, they can create a stored procedure for updating sales tables instead of writing the same SQL statement in different applications.
What are SQL commands?
Structured query language (SQL) commands are specific keywords or SQL statements that developers use to manipulate the data stored in a relational database. You can categorize SQL commands as follows.
Data definition language
Data definition language (DDL) refers to SQL commands that design the database structure. Database engineers use DDL to create and modify database objects based on the business requirements. For example, the database engineer uses the CREATE command to create database objects such as tables, views, and indexes.
Data query language
Data query language (DQL) consists of instructions for retrieving data stored in relational databases. Software applications use the SELECT command to filter and return specific results from a SQL table.
Data manipulation language
Data manipulation language (DML) statements write new information or modify existing records in a relational database. For example, an application uses the INSERT command to store a new record in the database.
Data control language
Database administrators use data control language (DCL) to manage or authorize database access for other users. For example, they can use the GRANT command to permit certain applications to manipulate one or more tables.
Transaction control language
The relational engine uses transaction control language (TCL) to automatically make database changes. For example, the database uses the ROLLBACK command to undo an erroneous transaction.
What is SQL injection?
SQL injection is a cyberattack that involves tricking the database with SQL queries. Hackers use SQL injection to retrieve, modify, or corrupt data in a SQL database. For example, they might fill in a SQL query instead of a person's name in a submission form to carry out a SQL injection attack.
Why is SQL important?
One common query language that is widely used in various kinds of applications is structured query language (SQL). SQL is a language that developers and data analysts learn and use because it works well with a variety of programming languages. For instance, they can create high-performing data processing applications using popular SQL database systems like Oracle or MS SQL Server by integrating SQL queries into Java code. SQL is also rather simple to understand because its statements make use of familiar English vocabulary.
History of SQL
On the foundation of the relational data model, SQL was created in the 1970s. The structured English query language (SEQUEL) was its original name. Later, the phrase was abbreviated to SQL. First to market with a commercial SQL relational database management system was Oracle, originally known as Relational Software.
What are the components of a SQL system?
Structured query language, or SQL, is used by relational database management systems for data administration and archiving. Many database tables that are related to one another are stored in the system. Relational database management systems include MS SQL Server, MySQL, and MS Access. These are the parts of a system like that.
How does SQL work?
Structured query language (SQL) implementation involves a server machine that processes the database queries and returns the results. The SQL process goes through several software components, including the following.
Parser
The parser starts by tokenizing, or replacing, some of the words in the SQL statement with special symbols. It then checks the statement for the following:
Correctness
The parser verifies that the SQL statement conforms to SQL semantics, or rules, that ensure the correctness of the query statement. For example, the parser checks if the SQL command ends with a semi-colon. If the semi-colon is missing, the parser returns an error.
Authorization
The parser also validates that the user running the query has the necessary authorization to manipulate the respective data. For example, only admin users might have the right to delete data.
Relational engine
The relational engine, or query processor, creates a plan for retrieving, writing, or updating the corresponding data in the most effective manner. For example, it checks for similar queries, reuses previous data manipulation methods, or creates a new one. It writes the plan in an intermediate-level representation of the SQL statement called byte code. Relational databases use byte code to efficiently perform database searches and modifications.
Storage engine
The storage engine, or database engine, is the software component that processes the byte code and runs the intended SQL statement. It reads and stores the data in the database files on physical disk storage. Upon completion, the storage engine returns the result to the requesting application.
What is MySQL?
MySQL is an open-source relational database management system offered by Oracle. Developers can download and use MySQL without paying a licensing fee. They can install MySQL on different operating systems or cloud servers. MySQL is a popular database system for web applications.
SQL vs. MySQL
Structured query language (SQL) is a standard language for database creation and manipulation. MySQL is a relational database program that uses SQL queries. While SQL commands are defined by international standards, the MySQL software undergoes continual upgrades and improvements.
What is NoSQL?
NoSQL refers to non-relational databases that don't use tables to store data. Developers store information in different types of NoSQL databases, including graphs, documents, and key-values. NoSQL databases are popular for modern applications because they are horizontally scalable. Horizontal scaling means increasing the processing power by adding more computers that run NoSQL software.
SQL vs. NoSQL
Structured query language (SQL) provides a uniform data manipulation language, but NoSQL implementation is dependent on different technologies. Developers use SQL for transactional and analytical applications, whereas NoSQL is suitable for responsive, heavy-usage applications.
What is a SQL server?
SQL Server is the official name of Microsoft's relational database management system that manipulates data with SQL. The MS SQL Server has several editions, and each is designed for specific workloads and requirements.