Re: IF() problem

[Jon Stephens]

A clarification. If a string value begins with a digit, MySQL does not 
convert it to zero (FALSE), but rather to an integer made up of the 
leading digits in the value (until a non-digit is reached). This can be 
shown by using the CAST() function.

mysql> SELECT '21b' = 0, CAST('21b' AS SIGNED);
+-----------+-----------------------+
| '21b' = 0 | CAST('21b' AS SIGNED) |
+-----------+-----------------------+
|         0 |                    21 |
+-----------+-----------------------+
1 row in set (0.00 sec)
However, if the string value begins with a non-digit, then it is coerced 
 or cast to zero:

mysql> SELECT 'b21' = 0, CAST('b21' AS SIGNED);
+-----------+-----------------------+
| 'b21' = 0 | CAST('b21' AS SIGNED) |
+-----------+-----------------------+
|         1 |                     0 |
+-----------+-----------------------+
1 row in set (0.00 sec)
It is still true that Przemyslaw was assuming that a non-empty string 
would always evaluate as TRUE, and this isn't necessarily the case. So 
the best strategy is to compare directly with the empty string, as 
already discussed.

Thanks to Paul DuBois for reminding me of this. My apologies to anyone 
whom I might have misled.

--
Jon Stephens, Technical Writer
MySQL AB   www.mysql.com
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