By Sergey Skudaev
You can use this web page to practice writing SQL select queries. Of cause, SQL queries are not limited just to select statement. There is update, delete and insert SQL statement, but SELECT SQL statement is the most important and most difficult to learn. Why SELECT SQL statement is most important. Because to write correct update or delete SQL statement, you must be able to select correct database record that you want to update or delete.
Let us imagine that we have a computer school where we teach different computer programming classes: Java, Visual basic, C++. For our computer school management, we created a database with the following tables.
One table is for teachers, one for students and one for computer courses. To link tables to each other, we created teachers-schedule table and students-courses table. Fields for these tables are shown in the table below:
For example, if we want to know which student is older than 21 and we write a query:
SELECT * FROM students WHERE age > 21
Or we want to get information a student whose first name is Michael:
SELECT * FROM students WHERE firstname='Michael'
You see how it is ease... Let us try something more complicated...
Students who take Java class:
SELECT students.firstname, students.lastname from students JOIN student_course ON students.studentid=student_course.studentid JOIN courses ON student_course.courseid=courses.courseid WHERE courses.coursename='Java'
The teacher name who teaches Java class:
SELECT t.firstname, t.lastname FROM teachers t JOIN schedule s ON t.teacherid=s.teacherid JOIN courses c ON s.courseid=c.courseid WHERE c.coursename='Java'
Copy the query, paste it in the text area and click Submit button. The query result will be displayed!"
I gave this page user only permission for executing select queries.
Try to write queries on your own. To find out what data is in any table execute query "SELECT * FROM [table name]"
1. Find which couses Michael Murphy is teaching.
2. Find which hours teaher Michael Murphy has classes.
3. Find which hours student Michael has classes.
3. Find what is student age in Java class.
4. Find at what hour PHP class starts.
|Your Query Result|
I wrote an eBook base on this page. It includes about 100 query examples:
Learn SQL Programming By Examples [Kindle Edition]2.99