On 10 Sep 2015, at 5:05pm, Nguyen Dang Quang <quangnd at gmail.com> wrote:
> In (4) the selected rows will have old or new values? Read this: <https://www.sqlite.org/isolation.html> "Within a single database connection X, a SELECT statement always sees all changes to the database that are completed prior to the start of the SELECT statement, whether committed or uncommitted. And the SELECT statement obviously does not see any changes that occur after the SELECT statement completes. But what about changes that occur while the SELECT statement is running? What if a SELECT statement is started and the sqlite3_step() interface steps through roughly half of its output, then some UPDATE statements are run by the application that modify the table that the SELECT statement is reading, then more calls to sqlite3_step() are made to finish out the SELECT statement? Will the later steps of the SELECT statement see the changes made by the UPDATE or not? The answer is that this behavior is undefined." In other words, even if you do some experiments and figure out which one SQLite is doing now for one specific query, do not depend on this behaviour staying the same in future versions of SQLite, or even for different queries in the same version of SQLite. If you want guaranteed consistent behaviour, do your operation in two different connections. Then the answer depends on whether you are using WAL mode or not. Simon.
