大约有 43,000 项符合查询结果（耗时：0.0357秒） [XML]
Retrieving the last record in each group - MySQL
...x, we can write greatest-n-per-group queries:
WITH ranked_messages AS (
SELECT m.*, ROW_NUMBER() OVER (PARTITION BY name ORDER BY id DESC) AS rn
FROM messages AS m
)
SELECT * FROM ranked_messages WHERE rn = 1;
Below is the original answer I wrote for this question in 2009:
I write the solu...
Face recognition Library [closed]
... you an idea of whats involved:
#include <ccv.h>
int main(int argc, char** argv)
{
ccv_dense_matrix_t* image = 0;
ccv_read(argv[1], &image, CCV_IO_GRAY | CCV_IO_ANY_FILE);
ccv_bbf_classifier_cascade_t* cascade = ccv_load_bbf_classifier_cascade(argv[2]); ccv_bbf_params_...
Converting RGB to grayscale/intensity
...th 32 bits i.e. 4 bytes per pixel
unsigned int fourBytes;
unsigned char r,g,b;
for (int index=0;index<width*height;index++)
{
fourBytes=pntrBWImage[index];//caches 4 bytes at a time
r=(fourBytes>>16);
g=(fourBytes>>8);
...
How can I run MongoDB as a Windows service?
...he following error: Cannot open MongoDB service
on computer '.'.
At line:1 char:1
+ Start-Service MongoDB
+ ~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : OpenError: (System.ServiceProcess.ServiceController:ServiceController) [Start-Service],
ServiceCommandException
+ FullyQualifiedError...
How can I select rows with most recent timestamp for each key value?
...r data. Each row has a sensor id, a timestamp, and other fields. I want to select a single row with latest timestamp for each sensor, including some of the other fields.
...
What is the purpose of Order By 1 in SQL select statement?
...number stands for the column based on the number of columns defined in the SELECT clause. In the query you provided, it means:
ORDER BY A.PAYMENT_DATE
It's not a recommended practice, because:
It's not obvious/explicit
If the column order changes, the query is still valid so you risk ordering ...
how to listen to N channels? (dynamic select statement)
...
You can do this using the Select function from the reflect package:
func Select(cases []SelectCase) (chosen int, recv Value, recvOK bool)
Select executes a select operation described by the list of cases. Like
the Go select statement, it bl...
must appear in the GROUP BY clause or be used in an aggregate function
...
Yes, this is a common aggregation problem. Before SQL3 (1999), the selected fields must appear in the GROUP BY clause[*].
To workaround this issue, you must calculate the aggregate in a sub-query and then join it with itself to get the additional columns you'd need to show:
SELECT m.cname...
Python nonlocal statement
...eavily indented when defining inner functions and ends up violating the 79 chars PEP8 recommendation. Any way to get around this problem? Can an inner function somehow be placed outside the outer function? I know the question sounds stupid, but I'm earnest.
– tommy.carstensen
...
SQL query to find record with ID not in another table
...
Try this
SELECT ID, Name
FROM Table1
WHERE ID NOT IN (SELECT ID FROM Table2)
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