Re: [Fwd: Result of UNION depends on order of fields in SELECT]

Vincenzo Ciaschini writes:
> consider the following database:
> CREATE TABLE t (
>   val1 int(11) default NULL,
>   vl2 int(11) default NULL
> ) TYPE=MyISAM;
> 
> --
> -- Dumping data for table 't'
> --
> 
> INSERT INTO t VALUES (1,2);
> INSERT INTO t VALUES (3,4);
> 
> Now execute this query:
> select val1, vl2 from t where val1=3 union select val1, vl2 from t where
> val1=1;
> 
> The result is:
> 
> +------+------+
> | val1 | vl2  |
> +------+------+
> |    3 |    4 |
> |    1 |    2 |
> +------+------+
> 2 rows in set (0.00 sec)
> 
> Correct
> 
> Now execute this query:
> 
> select val1, vl2 from t where val1=3 union select vl2, val1 from t where
> val1=1;
> 
> The result is:
> 
> +------+------+
> | val1 | vl2  |
> +------+------+
> |    3 |    4 |
> |    2 |    1 |
> +------+------+
> 2 rows in set (0.00 sec)
> 
> Wrong.
> 
> Shouldn't the union statement reorder the fields in the second select?
> 
> Bye,
>    Vincenzo

Hi!

No, union should not reorder columns.

Why would it be done ???

You will always get the columns in the order you asked.

-- 

Sincerely,

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