Question

I have the following table structure:

status: TINYINT

locked_by: INTEGER

date: DATETIME

page: TINYINT

my_id: BIGINTEGER

PRIMARY KEY IS (page, my_id)

and have the following indexes:

INDEX idx_col_lock_status (locked_by, status),

INDEX idx_my_id (my_id)

At some point we have the following rows:

status, locked_by, date, page, my_id

2       243        NULL  0     1
0       0          NULL  1     1
1       244        NULL  2     1
2       255        NULL  0     2
2       2556       NULL  1     2
2       255        NULL  2     2

I would like to update all rows (set status = 0, locked_by = )
that have their status value != 2 or

they have status value = 2 *but* there is

another row with the same my_id that has status != 2

After the above update the above rows should become.

status, locked_by, date, page, my_id

0       0          NULL  0     1   --note this line
0       0          NULL  1     1
0       0          NULL  2     1   --and this line
2       255        NULL  0     2
2       2556       NULL  1     2
2       255        NULL  2     2

I am using Mysql version 5.1.63.

Thanks

Answer 1

That should do it:

CREATE TEMPORARY TABLE tt(my_id int);
INSERT INTO tt SELECT my_id FROM yourTable WHERE status != 2);

UPDATE yourTable yt
SET yt.status = 0, yt.locked_by = 0
WHERE status != 2
OR 
(status = 2 AND EXISTS (SELECT 1 FROM tt WHERE yt.my_id = tt.my_id));

DROP TABLE tt;

You have to work with a temporary table here, because you can’t use the same table for update and a subquery.