大约有 45,000 项符合查询结果（耗时：0.0276秒） [XML]
COUNT(*) vs. COUNT(1) vs. COUNT(pk): which is better? [duplicate]
...for all your queries that need to count everything, even for joins, use *
SELECT boss.boss_id, COUNT(subordinate.*)
FROM boss
LEFT JOIN subordinate on subordinate.boss_id = boss.boss_id
GROUP BY boss.id
But don't use COUNT(*) for LEFT joins, as that will return 1 even if the subordinate table doe...
Why is C so fast, and why aren't other languages as fast or faster? [closed]
...what the machine does can be seen in the rules that govern the widening of char objects for use in expressions: whether the values of char objects widen to signed or unsigned quantities typically depends on which byte operation is more efficient on the target machine.
...
When to use Common Table Expression (CTE)
...ing well? Can someone give me a simple example of limitations with regular select, derived or temp table queries to make the case of CTE? Any simple examples would be highly appreciated.
...
Adding gif image in an ImageView in android
...= 0; i < 11; i++) {
app += (char) block[i];
}
if (app.equals("NETSCAPE2.0")) {
readNetscapeExt();
} e...
How do I check if an integer is even or odd? [closed]
...tring();
if (String.IsNullOrEmpty(foo))
return Evenness.Unknown;
char bar = foo[foo.Length - 1];
switch (bar)
{
case '0':
case '2':
case '4':
case '6':
case '8':
return Evenness.Even;
case '1':
case '3':
case '5':
case '7':
case...
Yes/No message box using QMessageBox
...lude <QApplication>
#include <QMessageBox>
int main(int argc, char **argv)
{
QApplication app{argc, argv};
while (QMessageBox::question(nullptr,
qApp->translate("my_app", "Test"),
qApp->translate("my_app", "...
Which is fastest? SELECT SQL_CALC_FOUND_ROWS FROM `table`, or SELECT COUNT(*)
...irm this - I just updated a query with 4 joins on a 168,000 row database. Selecting just the first 100 rows with a SQL_CALC_FOUND_ROWS took over 20 seconds; using a separate COUNT(*) query took under 5 seconds (for both count + results queries).
– Sam Dufel
Ju...
Check whether an input string contains a number in javascript
...pattern" is the regular expression itself, and "modifiers" are a series of characters indicating various options.
The character class is the most basic regex concept after a literal match. It makes one small sequence of characters match a larger set of characters. For example, [A-...
Using LIMIT within GROUP BY to get N results per group?
...to get all years into a single column, grouped by id and ordered by rate:
SELECT id, GROUP_CONCAT(year ORDER BY rate DESC) grouped_year
FROM yourtable
GROUP BY id
Result:
-----------------------------------------------------------
| ID | GROUPED_YEAR |...
Select all DIV text with single mouse click
How to highlight/select the contents of a DIV tag when the user clicks on the DIV...the idea is that all of the text is highlighted/selected so the user doesn't need to manually highlight the text with the mouse and potentially miss a bit of the text?
...