When will a stream query take effect?

[LuaKT]

Hi,
I'm wondering when a query that is executed with the fetch() function and returned as a stream is actually executed on the database.
For example, with this code:

let mut result_stream = sqlx::query!("SELECT * FROM t1 FOR UPDATE") // FOR UPDATE locks the row
    .fetch(&mut conn)
    .await?;

while let Some(x) = result_stream.try_next().await? {
    // ...
}

Will this lock all the rows in the table when the stream is returned from the query, or will it lock each row when I call try_next()?

Thanks

[abonander]

The query itself will be executed on the first call to .try_next().await as there is no .await? for .fetch().

It is at that point that the rows should be locked, although the exact details depend on the database.

Note that for the lock to be effective, the query needs to be executed in a transaction.