SQL Syntax
SQL Statements
SQL statements are used for the majority of tasks that need to be completed on a database.
Simple-to-understand keywords make up SQL statements.
A table called “Customers” has all of its records returned by the SQL statement that follows:
Example
Select all records from the Customers table:
SELECT * FROM Customers;
We will cover every topic regarding the various SQL statements in this course.
Database Tables
Most frequently, a database has one or more tables. Every table has a name (such as “Customers” or “Orders”) and is made up of records (rows) that hold data.
The well-known Northwind sample database, which is available in MS Access and MS SQL Server, will be used in this tutorial.
| 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 aforementioned table has seven columns (CustomerID, CustomerName, ContactName, Address, City, PostalCode, and Country) and five records (one for each customer).
Keep in Mind That...
- SQL keywords are NOT case sensitive: select is the same as SELECT
In this tutorial we will write all SQL keywords in upper-case.
Semicolon after SQL Statements?
Every SQL statement must terminate with a semicolon in certain database systems.
In database systems that let the execution of several SQL statements in a single request to the server, semicolons are typically used to divide each SQL statement.
Semicolons will be used at the conclusion of each SQL statement in this course.
Some of The Most Important SQL Commands
- SELECT – extracts data from a database
- UPDATE – updates data in a database
- DELETE – deletes data from a database
- INSERT INTO – inserts new data into a database
- CREATE DATABASE – creates a new database
- ALTER DATABASE – modifies a database
- CREATE TABLE – creates a new table
- ALTER TABLE – modifies a table
- DROP TABLE – deletes a table
- CREATE INDEX – creates an index (search key)
- DROP INDEX – deletes an index
