sqlite3, qmarks, and NULL values

[John Machin]

On May 20, 10:54 am, MRAB <goo... at mrabarnett.plus.com> wrote:
> Mitchell L Model wrote:
> > Suppose I have a simple query in sqlite3 in a function:
>
> >     def lookupxy(x, y):
> >         conn.execute("SELECT * FROM table WHERE COL1 = ? AND COL2 = ?",
> >                      (x, y))
>
> > However, COL2 might be NULL. I can't figure out a value for y that would retrieve rows for which COL2 is NULL. It seems to me that I have to perform an awkward test to determine whether to execute a query with one question mark or two.
>
> [snip]
> Have you tried None, ie lookupxy(x, None)?

Have *you* tried that? Here's another armchair philosopher's take on
the expected outcome:

EITHER:

the wrapper blindly causes this to appear like "... COL2 = NULL",
which won't/shouldn't work. "expression = NULL" is neither true nor
false, it's unknown. The WHERE clause will/should return no rows at
all.

Example of unknowableness of nullity using relops:

sqlite> select case when 1 = null then 'A' else 'B' end;
B
sqlite> select case when 1 <> null then 'A' else 'B' end;
B
Note that "1 = null" is not true AND "1 <> null" is not true either.

OR:

The wrapper cunningly but unadvertisedly is causing that to appear
like "... COL2 IS NULL"

Cheers,
John