2011/12/11 Michael Bayer <mike...@zzzcomputing.com> > My impression was Postgresql handles this much more nicely which is > confirmed by this post: > > http://beerpla.net/2009/02/17/swapping-column-values-in-mysql/ > > the usual way this kind of thing is done is via declaring local variables > in the SQL statement, and an example of doing such using MySQL's syntax is > in that linked article - MySQL will let you assign to the variable in the > WHERE clause so they do "update t set a=b, b=@temp where (@temp:=a) is not > null". This basically gets at the value of "a" before it changes, which > is what PG does in any case. > > None of this has much to do with SQLAlchemy, though. you'd pretty much > need to use a plain string or @compiles elements to produce that SQL within > SQLAlchemy. >
I know about correct behavior of postgresql in this task. And I was very surprising when found such "weird" behavior of mysql. Is this a bug in mysql? What tell sql standard about such operations? PS For now I made switch of column values in client code, by doing "select for update ..." and update each row of result. -- You received this message because you are subscribed to the Google Groups "sqlalchemy" group. To post to this group, send email to sqlalchemy@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
