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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.
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