/*
mysql> SELECT species, sex, COUNT(*) FROM Bird
-> WHERE species = 'dog' OR species = 'cat'
-> GROUP BY species, sex;
Empty set (0.00 sec)
*/
Drop table Bird;
CREATE TABLE Bird (
name VARCHAR(20),
owner VARCHAR(20),
species VARCHAR(20),
sex CHAR(1),
birth DATE,
death DATE
);
INSERT INTO Bird VALUES ('BlueBird','Joe','Car','f','1999-03-30',NULL);
INSERT INTO Bird VALUES ('RedBird','Yin','Bus','m','1979-04-30',1998-01-30);
INSERT INTO Bird VALUES ('RedBird','Yin','Bus','m','1998-01-30',NULL);
/* You need not retrieve an entire table when you use COUNT().
For example, the previous query, when performed just on dogs and
cats, looks like this:
*/
SELECT species, sex, COUNT(*) FROM Bird
WHERE species = 'dog' OR species = 'cat'
GROUP BY species, sex;