大约有 40,000 项符合查询结果（耗时：0.0813秒） [XML]
postgresql COUNT(DISTINCT …) very slow
...
You can use this:
SELECT COUNT(*) FROM (SELECT DISTINCT column_name FROM table_name) AS temp;
This is much faster than:
COUNT(DISTINCT column_name)
share
|
improve this answer
...
How do I build a numpy array from a generator?
...ess you either:
can predict how many elements it will yield when run:
my_array = numpy.empty(predict_length())
for i, el in enumerate(gimme()): my_array[i] = el
are willing to store its elements in an intermediate list :
my_array = numpy.array(list(gimme()))
can make two identical generators, ...
How do I update the notification text for a foreground service in Android?
... only by calling stopForground );
Example:
private static final int NOTIF_ID=1;
@Override
public void onCreate (){
this.startForeground();
}
private void startForeground() {
startForeground(NOTIF_ID, getMyActivityNotification(""));
}
private Notification getMyActivityNotification(String...
abort, terminate or exit?
...ers before it ends the program. These are registered with the atexit and on_exit functions.
std::terminate is what is automatically called in a C++ program when there is an unhandled exception. This is essentially the C++ equivalent to abort, assuming that you are reporting all your exceptional erro...
Calculate distance between two latitude-longitude points? (Haversine formula)
...
@Forte_201092: Because that is not necessary - as (sin(x))² equals (sin(-x))²
– Jean Hominal
May 30 '14 at 9:16
...
Preventing an image from being draggable or selectable without using JS
...it show no effect but still fire the drag event?
– Ty_
Sep 14 '15 at 17:49
6
I found I could stil...
Types in Objective-C on iOS
...
This is a good overview:
http://reference.jumpingmonkey.org/programming_languages/objective-c/types.html
or run this code:
32 bit process:
NSLog(@"Primitive sizes:");
NSLog(@"The size of a char is: %d.", sizeof(char));
NSLog(@"The size of short is: %d.", sizeof(short));
NSLog(@"The si...
How to exit pdb and allow program to continue?
...) clear 1
Deleted breakpoint 1
(Pdb) continue
Or, if you're using pdb.set_trace(), you can try this (although if you're using pdb in more fancy ways, this may break things...)
(Pdb) pdb.set_trace = lambda: None # This replaces the set_trace() function!
(Pdb) continue
# No more breaks!
...
Applying function with multiple arguments to create a new pandas column
...f = pd.DataFrame({"A": [10,20,30], "B": [20, 30, 10]})
>>> df['new_column'] = np.multiply(df['A'], df['B'])
>>> df
A B new_column
0 10 20 200
1 20 30 600
2 30 10 300
or vectorize arbitrary function in general case:
>>> def fx(x, y):
...
What version of javac built my jar?
...7. The version information is built in.
http://en.wikipedia.org/wiki/Java_class_file
Note: As mentioned in the comment below,
those bytes tell you what version the class has been compiled FOR, not
what version compiled it.
...