SQL Syntax

SQL Statements

The majority of database operations are executed using SQL statements, which are comprised of easily comprehensible keywords.

Below is an SQL statement that retrieves all records from a table named “Customers”:

Example

Retrieve all entries from the Customers table.

SELECT * FROM Customers;

This tutorial will comprehensively cover various SQL statements.

Database Tables

A typical database comprises one or more tables, each identified by a name (e.g., “Customers” or “Orders”), and holds records (rows) containing data.

In this tutorial, we will utilize the widely recognized Northwind sample database (available in MS Access and MS SQL Server).

Displayed below is a portion of the Customers table referenced in the examples:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

The displayed table comprises five records, each representing a distinct customer, and includes seven columns: CustomerID, CustomerName, ContactName, Address, City, PostalCode, and Country.

Keep in Mind That…

SQL keywords exhibit case insensitivity; hence, “select” is equivalent to “SELECT”.

Throughout this tutorial, we will render all SQL keywords in uppercase.

Semicolon after SQL Statements?

Certain database systems mandate a semicolon at the conclusion of each SQL statement.

The semicolon serves as the conventional means of delimiting individual SQL statements in systems permitting the execution of multiple SQL statements within the same server call.

Throughout this tutorial, we will adhere to using a semicolon at the conclusion of each SQL statement.

Some of The Most Important SQL Commands

SELECT: Retrieves data from a database.
UPDATE: Modifies existing data in a database.
DELETE: Removes data from a database.
INSERT INTO: Adds new data into a database.
CREATE DATABASE: Establishes a new database.
ALTER DATABASE: Adjusts the structure of a database.
CREATE TABLE: Generates a new table.
ALTER TABLE: Modifies the structure of a table.
DROP TABLE: Eliminates a table from the database.
CREATE INDEX: Establishes an index, facilitating efficient data retrieval.
DROP INDEX: Removes an index from the database.