大约有 44,000 项符合查询结果（耗时：0.0386秒） [XML]
MySQL COUNT DISTINCT
...
Select
Count(Distinct user_id) As countUsers
, Count(site_id) As countVisits
, site_id As site
From cp_visits
Where ts >= DATE_SUB(NOW(), INTERVAL 1 DAY)
Group By site_id
...
Why is it impossible to build a compiler that can determine if a C++ function will change the value
... /* modify variable */
variable = 1;
}
}
int main(int argc, char **argv) {
if (modifies_variable(f, variable)) {
printf("Modifies variable\n");
} else {
printf("Does not modify variable\n");
}
return 0;
}
...
Is there a good reason I see VARCHAR(255) used so often (as opposed to another length)?
...n multiple courses, books, and jobs, I have seen text fields defined as VARCHAR(255) as kind of the default for "shortish" text. Is there any good reason that a length of 255 is chosen so often, other than being a nice round number ? Is it a holdout from some time in the past when there was a goo...
Getting all selected checkboxes in an array
...
function get_selected_checkboxes_array(){ var ch_list=Array(); $("input:checkbox[type=checkbox]:checked").each(function(){ch_list.push($(this).val());}); ...
Update a table using JOIN in SQL Server?
...n table expression) - see here and here for more details:
;WITH t2 AS
(
SELECT [key], CalculatedColumn = SUM(some_column)
FROM dbo.table2
GROUP BY [key]
)
UPDATE t1
SET t1.CalculatedColumn = t2.CalculatedColumn
FROM dbo.table1 AS t1
INNER JOIN t2
ON t1.[key] = t2.[key];
The reas...
What is the advantage of using heredoc in PHP? [closed]
...e day I used to use them to construct SQL queries:
$sql = <<<SQL
select *
from $tablename
where id in [$order_ids_list]
and product_name = "widgets"
SQL;
To me this has a lower probability of introducing a syntax error than using quotes:
$sql = "
select *
from $tablename
where ...
Polymorphism in C++
...egorise them in various ways:
When is the polymorphic type-specific code selected?
Run time means the compiler must generate code for all the types the program might handle while running, and at run-time the correct code is selected (virtual dispatch)
Compile time means the choice of type-specif...
right click context menu for datagridview
...d like to rightclick on a row and have a menu pop up. Then i would like to select things such as copy, validate, etc
7 Answ...
How should one use std::optional?
...
@Rapptz Line 256: union storage_t { unsigned char dummy_; T value_; ... } Line 289: struct optional_base { bool init_; storage_t<T> storage_; ... } How is that not "a T and a bool"? I completely agree the implementation is very tricky and nontrivial, but conceptua...
Android: Coloring part of a string using TextView.setText()?
...eSpan(android.graphics.Typeface.BOLD);
// Set the text color for first 4 characters
sb.setSpan(fcs, 0, 4, Spannable.SPAN_INCLUSIVE_INCLUSIVE);
// make them also bold
sb.setSpan(bss, 0, 4, Spannable.SPAN_INCLUSIVE_INCLUSIVE);
yourTextView.setText(sb);
...