Re: quote and null

[Michael Stassen]

Paul DuBois wrote:
At 11:35 +1300 11/11/04, Toro Hill wrote:
Hi all.
I have question about how the function quote() works with NULL values. 
Here is what the mysql manual say:
---
QUOTE(str)
Quotes a string to produce a result that can be used as a properly 
escaped data value in an SQL statement. The string is returned 
surrounded by single quotes and with each instance of single quote 
(`''), backslash (`\'), ASCII NUL, and Control-Z preceded by a 
backslash. If the argument is NULL, the return value is the word 
``NULL'' without surrounding single quotes. The QUOTE() function was 
added in MySQL 4.0.3.

mysql> SELECT QUOTE('Don\'t!');
        -> 'Don\'t!'
mysql> SELECT QUOTE(NULL);
        -> NULL
<snip>
Does this seem correct? Have I missed or overlooked something?
No, I think this is a bug.  QUOTE(NULL) should return a string,
not a NULL value.  I've filed a bug report:
http://bugs.mysql.com/bug.php?id=6564
Why?  It is doing exactly as documented.  Quote is supposed to 
backslash-escape the given string.  NULL is not a string.  How do you 
backslash-escape a NULL string?  I think NULL is the only proper output of 
QUOTE(NULL), just as NULL is the only proper output of most functions when 
given NULL input (with the exception of the NULL-specific functions, of course).

  mysql> CREATE TABLE qt (s CHAR(10));
  Query OK, 0 rows affected (0.01 sec)
  mysql> INSERT INTO qt VALUES
      -> ('a string'),
      -> ('doesn\'t'),
      -> (NULL),
      -> ('C:\\dir1');
  Query OK, 4 rows affected (0.01 sec)
  Records: 4  Duplicates: 0  Warnings: 0
  mysql> SELECT s, QUOTE(s) FROM qt;
  +----------+------------+
  | s        | QUOTE(s)   |
  +----------+------------+
  | a string | 'a string' |
  | doesn't  | 'doesn\'t' |
  | NULL     | NULL       |
  | C:\dir1  | 'C:\\dir1' |
  +----------+------------+
  4 rows in set (0.00 sec)
Makes sense to me.
Michael
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