On Mon, 6 May 2013 23:53:40 +0100 Simon Slavin <slav...@bigfraud.org> wrote:
> > How do I create this kind of update statement? > > > > UPDATE T SET a=0.5*(a+b), b=0.5*(b-a); > > > > The RHS should always be used with the values of a and b before the > > assignment. > > > > I think that the result of this kind of statement is undefined, or? > > No need to worry, it will work the way you want it to work: > > The row is read. > The new values are calculated. > The new values are written to the database. ... > That was a terrible description. Actually that's not a bad approximation of what happens. Here's a simpler example: sqlite> create table t(a int, b int); sqlite> insert into t values (1,2); sqlite> select * from t; a b ---------- ---------- 1 2 sqlite> update t set a=b, b=a; -- Et Voila! sqlite> select * from t; a b ---------- ---------- 2 1 There is no "RHS". The syntax and semantics of SQL are its own; they cannot be extrapolated from other languages. --jkl _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
