Maximum-per-group problem for this table : Group « Select Clause « SQL / MySQL






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

Maximum-per-group problem for this table

      
mysql>
mysql>
mysql> CREATE TABLE mytable
    -> (
    ->  rec_id          INT UNSIGNED NOT NULL AUTO_INCREMENT,
    ->  name            VARCHAR(20) NOT NULL,
    ->  trav_date       DATE NOT NULL,
    ->  miles           INT NOT NULL,
    ->  PRIMARY KEY (rec_id)
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql>
mysql> INSERT INTO mytable (name,trav_date,miles)
    ->  VALUES
    ->          ('Ben','2010-11-30',152),
    ->          ('Suzi','2010-11-29',391),
    ->          ('Henry','2010-11-29',300),
    ->          ('Henry','2010-11-27',96),
    ->          ('Ben','2010-11-29',131),
    ->          ('Henry','2010-11-26',115),
    ->          ('Suzi','2010-12-02',502),
    ->          ('Henry','2010-12-01',197),
    ->          ('Ben','2010-12-02',79),
    ->          ('Henry','2010-11-30',203)
    -> ;
Query OK, 10 rows affected (0.00 sec)
Records: 10  Duplicates: 0  Warnings: 0

mysql>
mysql>
mysql> CREATE TABLE tmp
    -> SELECT name, MAX(trav_date) AS trav_date
    -> FROM mytable GROUP BY name;
Query OK, 3 rows affected (0.01 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql>
mysql> SELECT mytable.name, mytable.trav_date, mytable.miles
    -> FROM mytable, tmp
    -> WHERE mytable.name = tmp.name
    -> AND mytable.trav_date = tmp.trav_date
    -> ORDER BY mytable.name;
+-------+------------+-------+
| name  | trav_date  | miles |
+-------+------------+-------+
| Ben   | 2010-12-02 |    79 |
| Henry | 2010-12-01 |   197 |
| Suzi  | 2010-12-02 |   502 |
+-------+------------+-------+
3 rows in set (0.00 sec)

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

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

mysql>








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