Oracle 5.0 Reference Manual page 231

| snake | 1 |
+---------+----------+
Number of animals per sex:
mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex;
+------+----------+
| sex | COUNT(*) |
+------+----------+
| NULL | 1 |
| f | 4 |
| m | 4 |
+------+----------+
(In this output, indicates that the sex is unknown.)
NULL
Number of animals per combination of species and sex:
mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| bird | NULL |
| bird | f |
| cat | f |
| cat | m |
| dog | f |
| dog | m |
| hamster | f |
| snake | m |
+---------+------+----------+
You need not retrieve an entire table when you use
when performed just on dogs and cats, looks like this:
mysql> SELECT species, sex, COUNT(*) FROM pet
-> WHERE species = 'dog' OR species = 'cat'
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| cat | f |
| cat | m |
| dog | f |
| dog | m |
+---------+------+----------+
Or, if you wanted the number of animals per sex only for animals whose sex is known:
mysql> SELECT species, sex, COUNT(*) FROM pet
-> WHERE sex IS NOT NULL
-> GROUP BY species, sex;
+---------+------+----------+
| species | sex | COUNT(*) |
+---------+------+----------+
| bird | f |
| cat | f |
| cat | m |
| dog | f |
| dog | m |
| hamster | f |
| snake | m |
+---------+------+----------+
If you name columns to select in addition to the
present that names those same columns. Otherwise, the following occurs:
• If the
ONLY_FULL_GROUP_BY
mysql> SET sql_mode = 'ONLY_FULL_GROUP_BY';
Retrieving Information from a Table
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COUNT()
[538] SQL mode is enabled, an error occurs:
211
[970]. For example, the previous query,
COUNT()
[970] value, a
GROUP BY
clause should be