So far we have explained how to add data to tables and how to
change data. What remains is to discuss how to remove data that is
no longer needed. Just as adding data is only possible in whole
rows, you can only remove entire rows from a table. In the
previous section we discussed that SQL does not provide a way to
directly address individual rows. Therefore, removing rows can
only be done by specifying conditions that the rows to be removed
have to match. If you have a primary key in the table then you can
specify the exact row. But you can also remove groups of rows
matching a condition, or you can remove all rows in the table at
once.
You use the DELETE command to remove rows; the
syntax is very similar to the UPDATE command.
For instance, to remove all rows from the products table that have a price of 10, use
DELETE FROM products WHERE price = 10;
If you simply write
DELETE FROM products;
then all rows in the table will be deleted! Caveat programmer.
