DbSchema Tutorial | SQL Syntax

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In this section, we will discuss the basic syntax of SQL and familiarize ourselves with the most common SQL commands. SQL commands can be divided into a few major categories: DDL (Data Definition Language), DML (Data Manipulation Language), DQL (Data Query Language), and DCL (Data Control Language).

SQL Syntax

A SQL query must start with a command, like SELECT, UPDATE, DELETE, followed by a specification of where that command should take effect. SQL is not case-sensitive. However, conventionally, commands are written in uppercase.

A simple SQL query could be:

SELECT * FROM Customers;

In this query, SELECT is the command, * means all columns, and Customers is the name of the table we’re querying.

SQL Commands

Data Definition Language (DDL)

DDL commands are used to create, modify, or delete structures in the database.

• CREATE: This command is used to create a new table or a new database.

CREATE TABLE Customers (
    ID int,
    Name varchar(255),
    Email varchar(255),
    Address varchar(255)
);

• ALTER: This command is used to modify an existing database object like a table.

ALTER TABLE Customers ADD Email varchar(255);

• DROP: This command is used to delete a table or database.

DROP TABLE Customers;

Data Manipulation Language (DML)

DML commands are used for managing data within schema objects.

• INSERT: This command is used to insert data into a table.

INSERT INTO Customers (ID, Name, Email, Address)
VALUES (1, 'John Doe', '[email protected]', '123 Street, City');

• UPDATE: This command is used to modify existing records.

UPDATE Customers SET Email = '[email protected]' WHERE ID = 1;

• DELETE: This command is used to delete existing records.

DELETE FROM Customers WHERE ID = 1;

Data Query Language (DQL)

DQL commands are used to fetch data from the database.

• SELECT: This command is used to select data from a database. The data returned is stored in a result table, called the result-set.

SELECT * FROM Customers;
SELECT Name, Email FROM Customers WHERE ID = 1;

Data Control Language (DCL)

DCL commands are used to grant and revoke rights and permissions.

• GRANT: This command is used to give user’s access privileges to a database.

GRANT SELECT, INSERT, DELETE ON Customers TO 'user';

• REVOKE: This command is used to take back access privileges from a user.

REVOKE SELECT, INSERT, DELETE ON Customers FROM 'user';

Remember, these are the basic commands to get you started with SQL. The SQL language is quite vast and can handle complex queries and manipulations. As you become more comfortable with the basics, you can explore the more advanced areas of the language.

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