>>>> 2011/08/18 18:30 +0300, Marius Feraru >>>>
Thanks for your time reading my message, but I don't understand what
is the "result context" that you are talking about. Could you please
elaborate?
<<<<<<<<
Well, if an expression is an argument to, say, "CONCAT", the expression s result is character string. An argument to, say, "POW" is number. But the second and third arguments to "IF" have the same type, the type of the "IF" s context, and an expression that is an operand to "SELECT" may have any type: the result context does not require anything.

Now, your expression IF( DATE(d) = "some-date", TIME(d), d ) is an operand to "SELECT", and no type is required of it--but the types are not the same, wherefore there is at least one conversion, surely that the bare "d" is made character string. But it seems that instead "TIME(d)", a character string, is converted to some timestamp, a date. I wrote that I believe this an optimizer error because the least characterward tweak to this is enough to make it that which you seek: either concatenating empty string to "TIME(d)", thereby overriding any tendency the optimizer has to consider it other than a character string, or by concatenating empty string to the whole expression, thereby making the "IF" s result context character string, not any type.

Consider this:

-- 1) create test table containing a single DATETIME column
CREATE TABLE dt (d DATETIME);
-- 2) insert two test records
INSERT INTO dt VALUES ("2011-08-07 10:11:12"),("1234-05-06 07:08:09");

SELECT d, ADDTIME(IF( DATE(d)='2011-08-07', TIME(d), d), '1 1:1:1.000002') as x FROM dt;

The outcome is really screwy:

+---------------------+----------------------------+
| d | x |
+---------------------+----------------------------+
| 2011-08-07 10:11:12 | 2035-12-13 02:00:00 |
| 1234-05-06 07:08:09 | 1234-05-07 08:09:10.000002 |
+---------------------+----------------------------+

Surely there is a noteworthy bug here.


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