SQL workshop: DELETE statement

The DELETE statement in SQL is used to remove rows from a table based on a certain condition.

Syntax:

DELETE FROM table_name WHERE condition;

Important Points:

Safety First: Always backup your data before performing DELETE operations, especially on production data.
Use WHERE Clause Carefully: Without the WHERE clause, all rows in the table will be deleted!
Performance Consideration: If you are deleting many rows, it may be more efficient to create a new table with only the rows you want to keep, then rename the table.

Example: To delete all employees with the first name 'John' from an employees table:

DELETE FROM employees WHERE first_name = 'John';

Workshop Exercise:

Let's assume you have a table named students with the following data:

Exercise Tasks:

Basic Deletion:
- Delete the record of the student with the name "Charlie".
- After this operation, confirm that "Charlie" is no longer in the table.
Condition Deletion:
- Delete all students who have a grade less than 'C'.
- Confirm that only students with grades 'A' and 'B' remain in the table.
Full Deletion (CAUTION!):
- Delete all records from the students table.
- Confirm that the table is now empty.

Basic Deletion:

 DELETE FROM students WHERE name = 'Charlie';

Condition Deletion:

 DELETE FROM students WHERE grade > 'B';

After each task, participants can use the SELECT statement to view the table's contents and confirm their results:

SELECT * FROM students;

This exercise should give a practical understanding of how the DELETE statement works and the importance of using it with caution.