MySQL Bugs: #68993: SET IN UPDATE TABLE

Bug #68993	SET IN UPDATE TABLE
Submitted:	18 Apr 2013 6:51	Modified:	19 Apr 2013 8:03
Reporter:	Mohit Angiras	Email Updates:
Status:	Not a Bug	Impact on me:	None
Category:	MySQL Server: DML	Severity:	S3 (Non-critical)
Version:	5.5.15	OS:	Linux
Assigned to:		CPU Architecture:	Any

Description:
Table Structure:
+--------------+------------+------+-----+---------+-------+
| Field        | Type       | Null | Key | Default | Extra |
+--------------+------------+------+-----+---------+-------+
| LOGO_ID      | varchar(3) | NO   | PRI | NULL    |       | 
| LOGO_WIDTH   | varchar(3) | YES  |     | NULL    |       | 
| LOGO_HEIGHT  | varchar(3) | YES  |     | NULL    |       | 
| LOGO_ROWSPAN | varchar(1) | YES  |     | NULL    |       | 
+--------------+------------+------+-----+---------+-------+

Invalid query which still runs:
UPDATE  LOGO_DETAILS SET LOGO_HEIGHT='76' IS NULL;

results in wrong value updation.

Valid query:
UPDATE  LOGO_DETAILS SET LOGO_HEIGHT='76'

Why it still runs if it cannot update the right value.

How to repeat:

Also after Set <column-name> I can write any expression which has no meaning like:
 UPDATE  LOGO_DETAILS SET LOGO_HEIGHT='76' AND 'y' IS NULL;

While  

  UPDATE  LOGO_DETAILS SET LOGO_HEIGHT='76' AND 'y' IS NULL;

would usually not make much sense 

  '76' AND 'y' IS NULL

*is* a valid expression though which will evaluate to either
true of false and will be converted to 1 or 0 when assigned
to LOGO_HEIGHT

Your UPDATE above is the same as 

  UPDATE  LOGO_DETAILS SET LOGO_HEIGHT= ('76' AND 'y' IS NULL);

and your first queries equivalent is

  UPDATE  LOGO_DETAILS SET LOGO_HEIGHT= ('76' IS NULL);

As '76' clearly isn't NULL you're going to update all
LOGO_HEIGHT columns to the numeric value 0 with this
UPDATE

Agreed, there is no bug here.