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Is it possible to GROUP BY multiple columns using MySQL?
...red Dec 3 '09 at 17:14
Joe PhillipsJoe Phillips
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Oracle Differences between NVL and Coalesce
...om dual; would work as NVL will do an implicit conversion of numeric 10 to string.
select coalesce('abc',10) from dual; will fail with Error - inconsistent datatypes: expected CHAR got NUMBER
Example for UNION use-case
SELECT COALESCE(a, sysdate)
from (select null as a from dual
union
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How can I get a file's size in C++? [duplicate]
...of the c runtime library on Windows, Mac and Linux.
long GetFileSize(std::string filename)
{
struct stat stat_buf;
int rc = stat(filename.c_str(), &stat_buf);
return rc == 0 ? stat_buf.st_size : -1;
}
or
long FdGetFileSize(int fd)
{
struct stat stat_buf;
int rc = fstat(fd...
Do I need to heartbeat to keep a TCP connection open?
I have two components that that communicate via TCP/IP. Component A acts as a server/listener and Component B is the client. The two should communicate as quickly as possible. There can only ever be one connection at any time (though that is aside to this question). A senior developer at my comp...
浅谈TCP优化 - 更多技术 - 清泛网 - 专注C/C++及内核技术
...可以控制接收窗口的大小：
shell> sysctl -a | grep mem
net.ipv4.tcp_rmem = <MIN> <DEFAULT> <MAX>
如果我们出于传输性能的考虑，设置了一个足够大的缓冲，那么当大量请求同时到达时，内存会不会爆掉？通常不会，因为Linux本身有一个缓冲...
django admin - add custom form fields that are not part of the model
I have a model registered in the admin site. One of its fields is a long string expression. I'd like to add custom form fields to the add/update page of this model in the admin that based on these fields values I will build the long string expression and save it in the relevant model field.
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Downloading MySQL dump from command line
...backup.sql
You can even go as far as auto-compressing the output using gzip (if your DB is very big):
$ mysqldump -u [uname] -p db_name | gzip > db_backup.sql.gz
If you want to do this remotely and you have the access to the server in question, then the following would work (presuming the...
How are strings passed in .NET?
When I pass a string to a function, is a pointer to the string's contents passed, or is the entire string passed to the function on the stack like a struct would be?
...
string.split - by multiple character delimiter
i am having trouble splitting a string in c# with a delimiter of "][".
4 Answers
4
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PostgreSQL Crosstab Query
... the provided input query: row_name, category, value. There is no room for extra columns like in the 2-parameter alternative below.
Safe form
crosstab(text, text) with 2 input parameters:
SELECT *
FROM crosstab(
'SELECT section, status, ct
FROM tbl
ORDER BY 1,2' -- could also ju...