What happens when undef replaces a placeholder in SQL query?

[Mark]

What happens when a placeholder in an SQL statement is replaced by
undef/NULL?

E.g.,

SELECT fullname FROM people WHERE age = ?

$sth->execute()

Does this depend on the database? (DB2 in this case). Is this just an
error?

Thanks,
Mark

 

[Frank Seitz]

What happens when a placeholder in an SQL statement is replaced by
undef/NULL?

E.g.,

SELECT fullname FROM people WHERE age = ?

$sth->execute()

Does this depend on the database? (DB2 in this case). Is this just an
error?

No, it's not an error. It's simply an unsatisfiable condition,
because EXPR = NULL is false. I.e. you get an empty result set.
I think this behavior is the same under all relational database systems.

Frank

 

[Mark]

No, it's not an error. It's simply an unsatisfiable condition,
because EXPR = NULL is false. I.e. you get an empty result set.
I think this behavior is the same under all relational database systems.

Thanks Frank. We have a webapp that is executing a large/long query.
The DBA can 'see' the query as it is being executed, and it has a
number of '?' placeholders still in it. Some of the placeholder have
been replaced with specific values for the query, but a number of them
are still '?'. When this query is running, load on the DB server
shoots up, application responsiveness tanks, etc. So we are trying to
pinpoint the source of the problem.

Cheers,
Mark