Working with Grouped Data : Group « Select Clause « SQL / MySQL






  1. SQL / MySQL
  2. Select Clause
  3. Group

Working with Grouped Data

      
mysql>
mysql> CREATE TABLE BookOrders
    -> (
    ->     OrderID SMALLINT NOT NULL,
    ->     BookID SMALLINT NOT NULL,
    ->     Quantity SMALLINT NOT NULL,
    ->     PRIMARY KEY (OrderID, BookID)
    -> )
    -> ENGINE=INNODB;
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql>
mysql> INSERT INTO BookOrders VALUES
    -> (101, 13331, 1),
    -> (101, 12786, 1),
    -> (101, 16284, 2),
    -> (102, 19354, 1),
    -> (102, 15729, 3),
    -> (103, 12786, 2), (103, 19264, 1), (103, 13331, 1),
    -> (103, 14356, 2), (104, 19354, 1), (105, 15729, 1), (105, 14356, 2),
    -> (106, 16284, 2), (106, 13331, 1), (107, 12786, 3), (108, 19354, 1),
    -> (108, 16284, 4), (109, 15729, 1), (110, 13331, 2), (110, 12786, 2),
    -> (110, 14356, 2), (111, 14356, 2);
Query OK, 22 rows affected (0.00 sec)
Records: 22  Duplicates: 0  Warnings: 0

mysql>
mysql>
mysql> SELECT OrderID, SUM(Quantity) AS Total
    -> FROM BookOrders
    -> GROUP BY OrderID
    -> HAVING Total>(SELECT AVG(Quantity) FROM BookOrders);
+---------+-------+
| OrderID | Total |
+---------+-------+
|     101 |     4 |
|     102 |     4 |
|     103 |     6 |
|     105 |     3 |
|     106 |     3 |
|     107 |     3 |
|     108 |     5 |
|     110 |     6 |
|     111 |     2 |
+---------+-------+
9 rows in set (0.00 sec)

mysql>
mysql> drop table BookOrders;
Query OK, 0 rows affected (0.00 sec)








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36.Use the name column to place the rows in groups, but the summary functions operate on the miles values:
37.Parentheses may be used to group alternations.
38.To be more specific and find out how many messages each sender sent from each host, use two grouping columns.
39.Categorize groups on a logarithmic scale.
40.Missing and non-missing counts can be determined for subgroups as well.
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