10.删除数据

Rows can be removed from a table using the DELETE command. Suppose you
are no longer interested in the weather of Hayward. Then you can do the
following to delete those rows from the table:

DELETE FROM weather WHERE city = ‘Hayward’;

All weather records belonging to Hayward are removed.

SELECT * FROM weather;

city | temp_lo | temp_hi | prcp | date

—————+———+———+——+————

San Francisco | 46 | 50 | 0.25 | 1994-11-27

San Francisco | 41 | 55 | 0 | 1994-11-29

(2 rows)

One should be wary of statements of the form

DELETE FROM tablename;

Without a qualification, DELETE will remove all rows from the given
table, leaving it empty. The system will not request confirmation before
doing this!