Calculate the overall average and save it in a variable, then compare each driver's average to the saved value : Variable « Select Clause « SQL / MySQL






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

Calculate the overall average and save it in a variable, then compare each driver's average to the saved value

       
 using a HAVING clause
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 (0.01 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> SELECT @overall_avg := AVG(miles) FROM mytable;
+----------------------------+
| @overall_avg := AVG(miles) |
+----------------------------+
|              216.600000000 |
+----------------------------+
1 row in set (0.00 sec)

mysql> SELECT name, AVG(miles) AS driver_avg FROM mytable
    -> GROUP BY name
    -> HAVING driver_avg < @overall_avg;
+-------+------------+
| name  | driver_avg |
+-------+------------+
| Ben   |   120.6667 |
| Henry |   182.2000 |
+-------+------------+
2 rows in set (0.00 sec)

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








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