大约有 48,000 项符合查询结果（耗时：0.0406秒） [XML]
SQL - Rounding off to 2 decimal places
...
Seems to convert to string ? which screws up order by.
– blissweb
Mar 4 '18 at 2:08
2
...
Difference between Arrays.asList(array) and new ArrayList(Arrays.asList(array))
...l, if you overwrite an element, it gets overwritten in the original array, etc. Of course, some List operations aren't allowed on the wrapper, like adding or removing elements from the list, you can only read or overwrite the elements.
Note that the list wrapper doesn't extend ArrayList - it's a di...
Why does Iterable not provide stream() and parallelStream() methods?
...Streams.stream(Spliterators.spliteratorUnknownSize(iterator,
Spliterator.ORDERED))
And then Brian Goetz responded:
I think Sam's point was that there are plenty of library classes that
give you an Iterator but don't let you necessarily write your own
spliterator. So all you can do is ca...
How to profile a bash shell script slow startup?
...another version that can output nanoseconds), do this at the beginning of /etc/bash.bashrc (or wherever you'd like to begin a trace in any Bash script):
PS4='+ $(date "+%s.%N")\011 '
exec 3>&2 2>/tmp/bashstart.$$.log
set -x
add
set +x
exec 2>&3 3>&-
at the end of ~/.bas...
The ALTER TABLE statement conflicted with the FOREIGN KEY constraint
...e problem was, so I'll give a layman's example. If you have a table named 'Orders' and a table named 'Customers', and you've deleted some old customers, but not their orders, you will get this error if you decide to make a foreign key from Orders.CustomerId to Customers.Id. Some orders don't have a...
Throwing the fattest people off of an overloaded airplane.
...y heap!
var myHeap = new MinHeap<Passenger>(/* need comparer here to order by weight */);
foreach (var pass in passengers)
{
if (totalWeight < targetTotal)
{
// unconditionally add this passenger
myHeap.Add(pass);
totalWeight += pass.Weight;
}
else if...
Why doesn't os.path.join() work in this case?
...his is the primary purpose for folks using os.path.join. e.g. '/'.join(['/etc/', '/conf']) results in three slashes: '/etc///conf'
– Dustin Rasener
Jul 31 '12 at 14:03
18
...
Cron job every three days
... you want it to run on specific days of the month, like the 1st, 4th, 7th, etc... then you can just have a conditional in your script that checks for the current day of the month.
if (((date('j') - 1) % 3))
exit();
or, as @mario points out, you can use date('k') to get the day of the year inst...
Running a cron every 30 seconds
...ice.
Here is a simple example that logs "Hello World" every 10 seconds:
/etc/systemd/system/helloworld.service:
[Unit]
Description=Say Hello
[Service]
ExecStart=/usr/bin/logger -i Hello World
/etc/systemd/system/helloworld.timer:
[Unit]
Description=Say Hello every 10 seconds
[Timer]
OnBootSec=...
How do you find the row count for all your tables in Postgres
...mate:
SELECT schemaname,relname,n_live_tup
FROM pg_stat_user_tables
ORDER BY n_live_tup DESC;
That can also show you how many rows are dead, which is itself an interesting number to monitor.
The third way is to note that the system ANALYZE command, which is executed by the autovacuum proce...