Structured Query Language/DELETE 1

Hint: Be carefull and deactivate AUTOCOMMIT.

The DELETE command removes rows from a table.

DELETE FROM <tablename>
WHERE       <search_condition>;

The syntax is straightforward as we do not need to specify any column name - rows are deleted as a whole and not partly. As usual, the search condition specifies the criterion which identifies the affected rows. It can involve zero, one, or more rows. If we omit the WHERE keyword and the search condition all rows are affected.

Example

-- Delete one row
DELETE FROM person
WHERE  lastname = 'Burton';

-- It's only a test. Restore the row.
ROLLBACK;

The information about Mr. Burton was deleted and restored again.

Further Information

We present some more information about the DELETE command here. There are also some comments to the interconnection with the TRUNCATE command.

Exercises

Delete the hobby 'Yoga'.

Click to see solution

-- Delete one row
DELETE FROM hobby
WHERE  hobbyname = 'Yoga';
-- or: WHERE  id = 6;

ROLLBACK; -- if we want to restore the row
COMMIT;   -- if we want to commit our work

-- Check the result
SELECT * FROM hobby;

Delete all relations between persons and hobbies. Check result. Restore all rows.

Click to see solution

-- compact syntax - great impact
DELETE FROM person_hobby;

-- Check the result
SELECT * FROM person_hobby;

-- restore everything
ROLLBACK;