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I'm having the following problem using Django with MySQL 5.5.22. Given a table with columns id, level and a 2x2 matrix stored as a11, a12, a21, a22, I have this row: id a11 a12 a21 a22 level 324 3 2 5 3 2 Given a queryset qs, I do the following update: qs.update( a11=(b12 * a21 - b11 * a22) * F('a11') + (b11 * a12 - b12 * a11) * F('a21'), a12=(b12 * a21 - b11 * a22) * F('a12') + (b11 * a12 - b12 * a11) * F('a22'), a21=(b22 * a21 - b21 * a22) * F('a11') + (b21 * a12 - b22 * a11) * F('a21'), a22=(b22 * a21 - b21 * a22) * F('a12') + (b21 * a12 - b22 * a11) * F('a22'), level=(F('level') - 1) ) For which django generates the following query (got it from db.connection.queries, remove the where clause for brevity): UPDATE `storage` SET `a21` = (3 * `storage`.`a11`) + (-1 * `storage`.`a21`), `a22` = (3 * `storage`.`a12`) + (-1 * `storage`.`a22`), `level` = `storage`.`level` - -1, `a11` = (2 * `storage`.`a11`) + (-1 * `storage`.`a21`), `a12` = (2 * `storage`.`a12`) + (-1 * `storage`.`a22`) And my row looks like this after that: id a11 a12 a21 a22 level 324 2 1 4 3 1 For any row, a12*a21 - a11*a22 = 1 is supposed to be True, and according to that, the row was supposed to be: id a11 a12 a21 a22 level 324 1 1 4 3 1 This is what I get on SQLite, with Django generating the same query, and it took me a lot of time to figure that MySQL was doing something different. From the query, it seems like when updating interdepent multiple rows, MySQL doesn't treat it as a single atomic operation, and as columns are updated, they affect the values dependent on them. I confirmed this seems to be what happens by the following code on the Python prompt: >>> a11, a12, a2

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