Description:
Results of some tests for 4.1.11 and 5.0.3:
mysql> select @v, coercibility(@v);
+------+------------------+
| @v | coercibility(@v) |
+------+------------------+
| NULL | NULL |
+------+------------------+
1 row in set (0.00 sec)
mysql> set @v = null;
Query OK, 0 rows affected (0.00 sec)
mysql> select @v, coercibility(@v);
+------+------------------+
| @v | coercibility(@v) |
+------+------------------+
| NULL | 2 |
+------+------------------+
1 row in set (0.00 sec)
Here we check the coercibility for a variable that is NULL because it
has never been set, and for a variable that has been set to NULL explicitly.
The results are different.
Shouldn't the two results be the same? Or are these two NULL values
different in character somehow?
mysql> set @v = 1;
Query OK, 0 rows affected (0.01 sec)
mysql> select @v, coercibility(@v);
+------+------------------+
| @v | coercibility(@v) |
+------+------------------+
| 1 | 1 |
+------+------------------+
1 row in set (0.00 sec)
Variables that are set to a numeric value do not have IMPLICIT
coercibility. (This means that the "always IMPLICIT" principle is
not true, unless this result is a bug.)
mysql> set @v = now();
Query OK, 0 rows affected (0.00 sec)
mysql> select @v, coercibility(@v);
+---------------------+------------------+
| @v | coercibility(@v) |
+---------------------+------------------+
| 2005-03-01 08:41:18 | 2 |
+---------------------+------------------+
1 row in set (0.00 sec)
Okay, this is IMPLICIT ... presumably because the temporal value is converted
to a string when stored in the user variable?
mysql> set @v = binary 'a';
Query OK, 0 rows affected (0.00 sec)
mysql> select @v, coercibility(@v);
+------+------------------+
| @v | coercibility(@v) |
+------+------------------+
| a | 2 |
+------+------------------+
1 row in set (0.01 sec)
mysql> set @v = 'a';
Query OK, 0 rows affected (0.00 sec)
mysql> select @v, coercibility(@v);
+------+------------------+
| @v | coercibility(@v) |
+------+------------------+
| a | 2 |
+------+------------------+
1 row in set (0.00 sec)
Okay, these are IMPLICIT, too. I take it that if the value assigned
to the variable is a string, it doesn't matter whether it's a binary
or non-binary string, or what the collation is for a non-binary string?
(That is, is it the case that *any* kind of string assigned to a user
variable results in the variable having IMPLICIT coercibility?)
How to repeat:
Runt the above queries.
