QueryRow doesn't work as documented

[mikewilliamson]

I'm using this fragment of code, which is taken almost verbatim from the example given in the QueryRow documentation:

var Id int
err = db.QueryRow("select max(EventId) from Event").Scan(&Id)
switch {
case err == sql.ErrNoRows:
    log.Printf("No EventId.")
case err != nil:
    log.Fatal(err)
default:
    fmt.Printf("Max EventId is %v\n", Id
}

According to the docs, you would expect the message No EventId, but what you get is this:

2015/09/11 10:38:53 sql: Scan error on column index 0: converting string "<nil>" to a int: strconv.ParseInt: parsing "<nil>": invalid syntax

Is this a bug in the driver, or in the sql package?

[dimdin]

@mikewilliamson what is the database type of Event.EventId ?

[dimdin]

@mikewilliamson I can reproduce it with the code:

func TestBug126(t *testing.T) {
    conn := open(t)
    defer conn.Close()
    var Id int
    err := conn.QueryRow("select null").Scan(&Id)
    if err != nil {
        t.Fatal("Cannot scan to int: ", err.Error())
    }
}

select max(EventId) from Event is going to return null when there are no records in Event.
You can not scan a null value to int, so this is not a bug.
To solve your problem try this query:

select max(EventId) from Event where exists (select 1 from Event)

[mikewilliamson]

Ah, got it, thanks. I was mistakenly thinking that the query would return no rows rather than one row with a null. My mistake. Actually what I want is something like:

select isnull(max(EventId), 0) from Event