大约有 45,000 项符合查询结果（耗时：0.0303秒） [XML]
How expensive is RTTI?
...ases with optimisation, typeid() is nearly x20 faster than dyncamic_cast.
Chart
The Code
As requested in the comments, the code is below (a bit messy, but works). 'FastDelegate.h' is available from here.
#include <iostream>
#include "FastDelegate.h"
#include "cycle.h"
#include "time.h"
// U...
PostgreSQL - fetch the row which has the Max value for a column
...sted index lookup into lives - on my machine
-- the latter query plan was selected given my memory settings and
-- histogram
SELECT
l1.*
FROM
lives AS l1
INNER JOIN (
SELECT
usr_id,
MAX(time_stamp) AS time_stamp_max
FROM
lives
GROUP BY
usr_id
) AS l2
...
Postgres: INSERT if does not exist already
...onditional INSERT in PostgreSQL:
INSERT INTO example_table
(id, name)
SELECT 1, 'John'
WHERE
NOT EXISTS (
SELECT id FROM example_table WHERE id = 1
);
CAVEAT This approach is not 100% reliable for concurrent write operations, though. There is a very tiny race condition between...
Select distinct using linq [duplicate]
...
myList.GroupBy(test => test.id)
.Select(grp => grp.First());
Edit: as getting this IEnumerable<> into a List<> seems to be a mystery to many people, you can simply write:
var result = myList.GroupBy(test => test.id)
.S...
How do I UPDATE from a SELECT in SQL Server?
... SQL Server , it is possible to insert rows into a table with an INSERT.. SELECT statement:
35 Answers
...
SQL Server: SELECT only the rows with MAX(DATE)
...
If rownumber() over(...) is available for you ....
select OrderNO,
PartCode,
Quantity
from (select OrderNO,
PartCode,
Quantity,
row_number() over(partition by OrderNO order by DateEntered desc) as rn
from YourTable) a...
ASP.NET Identity reset password
...
Thank you for your answer. It works like a charm for me.
– Thomas.Benz
Mar 16 '17 at 13:43
4
...
selecting unique values from a column
...
Use the DISTINCT operator in MySQL:
SELECT DISTINCT(Date) AS Date FROM buy ORDER BY Date DESC;
share
|
improve this answer
|
follow
...
How to split a delimited string in Ruby and convert it to an array?
...
whitespace, with leading whitespace and runs of contiguous whitespace
characters ignored.
If pattern is a Regexp, str is divided where the pattern matches.
Whenever the pattern matches a zero-length string, str is split into
individual characters. If pattern contains groups, the respec...
How to reuse an ostringstream?
...ct of the deprecated std::strstream, which was able to write directly to a char array you allocated on the stack. You had to insert a terminating null manually. However, std::ends is not deprecated, i think because it's still useful as in the above cases.
...