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"О дне же том, или часе, никто не знает, ни Ангелы небесные, ни Сын, но только Отец (Мк. 13, 32)"

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???? ?????? ????? ???????????? ??? ????????? ?????? ?? ??????? ????: ``??? ????? ?????? ????????????? ???? ??????????? ? ????????'' ???, ????????, ????? ???????????? ?????? ????? ?????????? ????????, ??? ??, ??????? ???????? ??????? ? ??????? ?? ??????????, ??? ???????? ?????????????? ???????????? ?? ???? ?????????? ??????????.
????????? ???????? ?????????? ???????? ? ???????? ????????? ???????? ?????????? ????? ? ???????, ??? ??? ?? ?????? ???????? ?????????? ?? ????? ??????. ??????? COUNT() ?????????? ?????????? ???????? ???????????, ? ? ?? ??????? ????? ????????? ????????? ?????? ??? ??????????? ????? ????????:

mysql> SELECT COUNT(*) FROM pet;
+----------+
| COUNT(*) |
+----------+
|        9 |
+----------+

????? ?? ??? ????????? ?? ??????? ????? ?????????? ????????. ??? ?????? ??????? COUNT() ????? ??????, ??????? ???????? ??????????? ??????? ?? ??????????:

mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner;
+--------+----------+
| owner  | COUNT(*) |
+--------+----------+
| Benny  |        2 |
| Diane  |        2 |
| Gwen   |        3 |
| Harold |        2 |
+--------+----------+

???????? ???????? ?? ????????????? ??????? GROUP BY ??? ??????????? ???? ??????? ?? ??????? ?? ??????????. ??? ???? ??????? ?????? ????? ?? ?????? ????????? ?? ??????:

mysql> SELECT owner, COUNT(owner) FROM pet;
ERROR 1140 at line 1: Mixing of GROUP columns (MIN(),MAX(),COUNT()...)
with no GROUP columns is illegal if there is no GROUP BY clause

??????? COUNT() ? GROUP BY ????? ???????? ??????????????? ?????? ?????????? ?????????. ? ????????, ??????????? ????, ?? ??????? ? ?????? ??????? ?????????? ?????????????? ?????????.

?????????? ???????? ??????? ????:

mysql> SELECT species, COUNT(*) FROM pet GROUP BY species;
+---------+----------+
| species | COUNT(*) |
+---------+----------+
| bird    |        2 |
| cat     |        2 |
| dog     |        3 |
| hamster |        1 |
| snake   |        1 |
+---------+----------+

?????????? ???????? ??????? ????:

mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex;
+------+----------+
| sex  | COUNT(*) |
+------+----------+
| NULL |        1 |
| f    |        4 |
| m    |        4 |
+------+----------+

(? ???? ??????? ??????????? NULL ??????????, ??? ??? ????????? ??????????)

?????????? ???????? ??????? ???? ? ?????? ????:

mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex;
+---------+------+----------+
| species | sex  | COUNT(*) |
+---------+------+----------+
| bird    | NULL |        1 |
| bird    | f    |        1 |
| cat     | f    |        1 |
| cat     | m    |        1 |
| dog     | f    |        1 |
| dog     | m    |        2 |
| hamster | f    |        1 |
| snake   | m    |        1 |
+---------+------+----------+

??? ????????????? ??????? COUNT() ????? ?? ??????????? ????????? ??? ???????. ????????, ?????????? ??????, ? ??????? ??????????? ?????? ????? ? ??????, ???????? ????????? ???????:

mysql> SELECT species, sex, COUNT(*) FROM pet
    -> WHERE species = "dog" OR species = "cat"
    -> GROUP BY species, sex;
+---------+------+----------+
| species | sex  | COUNT(*) |
+---------+------+----------+
| cat     | f    |        1 |
| cat     | m    |        1 |
| dog     | f    |        1 |
| dog     | m    |        2 |
+---------+------+----------+

????? ?????? ? ?????????? ???????? ??????? ???? ? ?????? ?????? ??? ???????????, ??? ??????? ????????:

mysql> SELECT species, sex, COUNT(*) FROM pet
    -> WHERE sex IS NOT NULL
    -> GROUP BY species, sex;
+---------+------+----------+
| species | sex  | COUNT(*) |
+---------+------+----------+
| bird    | f    |        1 |
| cat     | f    |        1 |
| cat     | m    |        1 |
| dog     | f    |        1 |
| dog     | m    |        2 |
| hamster | f    |        1 |
| snake   | m    |        1 |
+---------+------+----------+

<!--UdmComment-->

User Comments

Posted by Daryl Luk on January 6 2004 8:23am[Delete] [Edit]

The GROUP BY clause yields different result between MySQL 4.0.17 and Oracle 8i (didn't check SQL Server).

Given a table "items":

mysql&gt; select * from items;

+------+------+-------+
| name | cost | owner |
+------+------+-------+
| pen | 10 | tom |
| ink | 15 | tom |
| book | 20 | pete |
+------+------+-------+
3 rows in set (0.00 sec)

Using the following SELECT statement:

SELECT name, sum(cost) FROM items BROUP BY owner;

Oracle will detect an error saying not a GROUP BY expression

but MySQL gives a result:

+------+-----------+
| name | sum(cost) |
+------+-----------+
| book | 20 |
| pen | 25 |
+------+-----------+
2 rows in set (0.01 sec)

Oracle seems to be correct since the "name" column could not really be GROUP BY "owner".

Any comment...

Add your own comment.






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Внимание! Читая пророчества на этом сайте помните что достоверность трудно проверить и все может во времени изменяться
"О дне же том, или часе, никто не знает, ни Ангелы небесные, ни Сын, но только Отец (Мк. 13, 32)"