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From:Dan Nelson Date:September 19 2010 6:09am
Subject:Re: Too Strange for Words
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In the last episode (Sep 18), Victor Subervi said:
> Can someone please explain to me why Passengers.weight comes up null for
> the last value sometimes, and other times it comes up with the value 155??

Passengers id 1 through 3 have a weight of NULL in the Passengers table, and
passenger 4 has a weight of 155.  Your first query ends up returning rows
for only matches passengers 1 through 3, so you will always get NULL in the
weight column.  What were you expecting to see?
 
> mysql> select p.id, c.id, p.name, p.weight, m.amount, p.round_trip,
> c.first_name, c.middle_name, c.last_name, c.suffix, c.sex, p.confirmation,
> m.type, m.payment, p.late_fee, p.late_fee_paid, m.discount from Passengers p
> join Customers c join Money m on m.foreign_id=p.id and
> m.customer_id=c.idwhere m.type="flight fee" and p.flight_id=1;
>
> +----+----+------+--------+--------+------------+------------+-------------+-----------+--------+------+--------------+------------+---------+----------+---------------+----------+
> | id | id | name | weight | amount | round_trip | first_name | middle_name |
> last_name | suffix | sex  | confirmation | type       | payment | late_fee | late_fee_paid
> | discount |
>
> +----+----+------+--------+--------+------------+------------+-------------+-----------+--------+------+--------------+------------+---------+----------+---------------+----------+
> |  1 |  1 | NULL |   NULL |  70.00 |          0 | Adolph     | NULL        | Hitler  
>  | NULL   | Male | 123456       | flight fee | CC      | no       | n/a           |       
> 0 |
> |  2 |  1 | NULL |   NULL |  70.00 |          0 | Adolph     | NULL        | Hitler  
>  | NULL   | Male | 987987987    | flight fee | cash    | no       | n/a           |       
> 0 |
> |  3 |  3 | NULL |   NULL |  70.00 |          0 | Me         | NULL        | Too     
>  | NULL   | Male | 123456       | flight fee | CC      | no       | n/a           |      
> 20 |
>
> +----+----+------+--------+--------+------------+------------+-------------+-----------+--------+------+--------------+------------+---------+----------+---------------+----------+
> 3 rows in set (0.00 sec)
> 
> mysql> select * from Passengers;
>
> +----+-----------+-------------+------+------+--------+-------+------------+--------------+----------+---------------+
> | id | flight_id | customer_id | name | sex  | weight | price | round_trip |
> confirmation | late_fee | late_fee_paid |
>
> +----+-----------+-------------+------+------+--------+-------+------------+--------------+----------+---------------+
> |  1 |         1 |           1 | NULL | Male |   NULL |  0.00 |          0 | 123456  
>     | no       | n/a           |
> |  2 |         1 |           1 | NULL | Male |   NULL |  0.00 |          0 |
> 987987987    | no       | n/a           |
> |  3 |         1 |           2 | NULL | Male |   NULL |  0.00 |          0 | 123456  
>     | no       | n/a           |
> |  4 |         1 |           3 | NULL | Male |    155 | 70.00 |          0 | 123456  
>     | no       | n/a           |
>
> +----+-----------+-------------+------+------+--------+-------+------------+--------------+----------+---------------+
> 4 rows in set (0.00 sec)
> 
> mysql> select p.weight from Passengers p;
> +--------+
> | weight |
> +--------+
> |   NULL |
> |   NULL |
> |   NULL |
> |    155 |
> +--------+
> 4 rows in set (0.00 sec)
> 
> TIA,
> Victor

-- 
	Dan Nelson
	dnelson@stripped
Thread
Too Strange for WordsVictor Subervi18 Sep
  • Re: Too Strange for WordsDan Nelson19 Sep