Toggle a Bit with SQL

January 04, 2007
databasesweb

I am working on a management dashboard for a client, which uses some AJAX here and there. One simple but really nice feature is that you can enabled or disable things just by clicking on an icon, the state is updated in the background using AJAX (I also add some animation to let the user know that it has been updated).

shows the transition of states

I wanted to be able to toggle the state of the bit field without a care of the current state. Here's how you can do that in SQL:

UPDATE companies
SET active_ind = active_ind ^ 1
WHERE id = ?

I'm using a ^ Bitwise (Exclusive OR or XOR) operator here to do this. To understand what's going on here let's look at a truth table for XOR:

p q p ^ q
1 1 0
1 0 1
0 1 1
0 0 0


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Uh... 0 ^ 0 = 0
Why not: SET active_ind = 1 - active_ind ?
Oops thanks Neil, I was copying and pasting the rows of hmtl, and forgot to change the last one... Fixed.
Rick that's a good solution as well, and probably a bit more readable. Thanks!
SET active_ind = 1 - active_ind Does that work? 1 - 0 = 0 0 - 1 = -1 does this end up as bit 1
Nice tip! I have never used bit-wise manipulation in SQL. It's something I should look into.
Dale, yes it does work: 1 - 0 = 1 1 - 1 = 0
if 1 is always 1 then you can use the NOT option to revse the value of active_ind. UPDATE companies SET active_ind = ~active_ind WHERE id = ?
Very elegant. I have been using the ternary operator in PHP, but that requires passing in a variable from the middleware tier. I'll be using this from now on.
Hi, I have a similar problem: I have been banging my head with this one. Problem: I have a SQL Query that sets a bit in a field (I didn't write the query) Code: UPDATE Table_name SET Options=Options|16 WHERE field='value' And Also Code: UPDATE table_name SET Options=Options|8|4|64|128 WHERE field='value' I was told this is setting the bit flags in the field and this query does work correctly. My Question is: How do I reverse the bit settings? I was told to use the ampersand "&" but it didn't work as I had thought. So if I set options|16 I can unset options|16 Thanks in advance -------------------------- so I found the the Tilda "~" (without the quotes) is the reverse binary option, but it didn't do as I thought it would :-(
Try Options & ~16. Basically, you want to invert 16, then AND it with your options: 16 = 0001 0000 ~ = 1110 1111 If Options is 217 = 1101 1001 SELECT Options & ~16 will give: 201 = 1100 1001
Use ABS to get the absolute value (-1 becomes 1)...

DECLARE @Trend AS BIT
SET @Trend = 0
SELECT @Trend, ABS(@Trend-1)
ROFL

since when it turned into 0-1

LOLZ
To toggle a bit in a bitfield in your table, try this:
UPDATE user SET vis=IF(vis&4,vis&~4,vis|4) WHERE id=$authuserid LIMIT 1

The value "4" can be replaced with 2^bitposition, ie. 1,2,4,8,16,32,64...

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