Kevin Piciulo <[EMAIL PROTECTED]> wrote:
> Hello,
> I've been staring at this line for quite a while now, and can't
> figure out what the problem is. I know the database is created and
> open. The following returns SQLITE_ERROR.
>
> sqlite3_prepare(m_dbDataBase, "UPDATE Users SET ? = ? WHERE user_id ==
> ?;", -1, &stmt, NULL);
>
> My guess is that i can't use a variable to represent the column name.
> Is this the case?
Your guess is right. You can only use a variable in places
where it is valid to put an expression. You cannot say
UPDATE users SET 5+x = 22.7/y ...
because the expression "5+x" is not valid in that context.
So that means you cannot put a variable there either.
The sqlite3_prepare() routine actually invokes a compiler
that translates your SQL statement into bytecode that will
implement the statement. The "?" tokens get translated into
a load-immediate kind of instruction where the value to
be loaded is supplied by a subsequent sqlite3_bind_... call.
The value to be loaded defaults to NULL.
Changes to the column name on the left-hand side of the
assignment cause different code to be generated, and
sqlite3_bind_... calls do not have the ability to recompile
the bytecode to accomodate the change.
--
D. Richard Hipp <[EMAIL PROTECTED]>
