Question

I have a an sqlite database with the table test. Several processes are accessing this database from bash. The table has the following fields:

CREATE TABLE mytable (id NUMERIC,
start JULIAN,
finish JULIAN)

I obtain an unique id by:

id=$(sqlite test.db <<EOF
BEGIN EXCLUSIVE;
SELECT id FROM mytable WHERE start IS NULL ORDER BY RANDOM() LIMIT 1;
COMMIT;
EOF
)

My question is, how can update the field start with:

UPDATE mytable set start=julianday('now') where id="SELECTED ID FROM ABOVE";

In the same statement?

Answer 1

Based on the comments that you supplied above, my solution would look something like follows (in perl with a raw DBI connection, also i didn’t do a lot of error checking or anything either, something that you should probably do):

my $dbh = DBI->connect(...);
$dbh->do("BEGIN EXCLUSIVE");
my $stm = $dbh->prepare("SELECT id FROM mytable WHERE start IS NULL ORDER BY RANDOM() LIMIT 1");
$stm->execute();
my $row = $stm->fetchrow_hashref();
my $id = undef;
if ( $row ) {
    $id = $row->{ID};
    my $ustm = $dbh->prepare("UPDATE mytable set start=julianday('now') where id=?");
    $ustm->execute($id);
}
$dbh->do("COMMIT");
# Still have the id at this point.