Structured Query Language (SQL) is a standard language for storing, manipulating and retrieving data in databases. With these few lessons, you will learn SQL in less than 3 hours.
Introduction to databases
In the first step, I will present a few theoretical issues about databases. This knowledge is necessary in order to be able to design databases and then use the SQL language.
CREATE TABLE
After learning the theoretical issues, it is time to create a database and tables. We will use SQL language for this purpose. In this lesson you will learn the commands: CREATE TABLE, CREATE DATABASE, and you will also learn a little about the data types.
INSERT INTO
Once we have the tables, it's time to put some data into them. In this lesson you will learn the INSERT INTO command.
SELECT, FROM and ORDER BY
If you have tables and data in tables, you can start displaying these data. In this lesson you will learn the commands: SELECT, FROM and ORDER BY. The SELECT command allows you to display data stored in one or more tables. FROM clause is used to list the tables and any joins required for the SQL statement. ORDER BY clause is used to sort the records in the result set for a SELECT statement.
WHERE
WHERE clause is used to filter the results and apply conditions in a SELECT, UPDATE, or DELETE statement. With this clause you can only view the data you are interested in.
JOINS
JOINS are used to retrieve data from multiple tables. A SQL JOIN is performed whenever two or more tables are listed in a SQL statement. There are four types of joins: INNER JOIN, LEFT OUTER JOIN, RIGHT OUTER JOIN, FULL OUTER JOIN.
GROUP BY, HAVING and aggregate functions
Data stored in tables can be grouped. To achieve this, the GROUP BY clause must be used. In this lesson, apart from GROUP BY clause, you will also learn HAVING clause and aggregating functions such as MIN, MAX, AVG, COUNT.
UNIONS
This lesson explains how to use the UNION, UNION ALL, EXCEPT and INTERSECT operator with examples. These operators are used for slightly different table combinations than JOINS.
Subqueries
Sometimes it is necessary to write one query inside another query. Such internal queries are called subqueries. And this lesson will be about subqueries. Subqueries can be changed into JOINS and JOINS can be changed into subqueries.
Useful functions
When we display data, very often it is necessary to format it properly, or connect or cut a piece of data. In this case, the functions that SQL offers are useful. In this lesson we will learn about the most commonly used functions.
Update, Alter, Drop, Delete and Truncate
Once you've learned to display and insert data, it's time to learn how to modify and delete data. In this lesson you will learn about Update, Alter, Drop, Delete and Truncate commands.
VIEWS
The VIEW is, in essence, a virtual table that does not physically exist. Rather, it is created by a SQL statement that joins one or more tables. In this lesson you will learn to work with views, create, modify and delete them.