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count(*) vs count(column-name) - which is more correct? [duplicate]
... difference is:
COUNT(*) will count the number of records.
COUNT(column_name) will count the number of records where column_name is not null.
Therefore COUNT(*) is what you should use. If you're using MyISAM and there is no WHERE clause, then the optimiser doesn't even have to look at the tabl...
Is it safe to use -1 to set all bits to true?
...alue you need, to initialize a to the highest possible value, is -1 or UINT_MAX. The second will depend on the type of a - you will need to use ULONG_MAX for an unsigned long. However, the first will not depend on its type, and it's a nice way of getting the most highest value.
We are not talking a...
Static link of shared library function in gcc
...ent the name of the binary you want make portable, for example: nmap
./cde_2011-08-15_64bit nmap
The program will read all of libs linked to nmap and its dependencias and it will save all of them in a folder called cde-package/ (in the same directory that you are).
Finally, you can compress the...
Automatically add all files in a folder to a target using CMake?
...
It is possible. E.g. with file(GLOB:
cmake_minimum_required(VERSION 2.8)
file(GLOB helloworld_SRC
"*.h"
"*.cpp"
)
add_executable(helloworld ${helloworld_SRC})
Note that this requires manual re-running of cmake if a source file is added or removed, since t...
How do I restore a dump file from mysqldump?
...
It should be as simple as running this:
mysql -u <user> -p < db_backup.dump
If the dump is of a single database you may have to add a line at the top of the file:
USE <database-name-here>;
If it was a dump of many databases, the use statements are already in there.
To run the...
Check to see if python script is running
...stem is using domain sockets:
import socket
import sys
import time
def get_lock(process_name):
# Without holding a reference to our socket somewhere it gets garbage
# collected when the function exits
get_lock._lock_socket = socket.socket(socket.AF_UNIX, socket.SOCK_DGRAM)
try:
...
Trying to start a service on boot on Android
...> element:
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
In your <application> element (be sure to use a fully-qualified [or relative] class name for your BroadcastReceiver):
<receiver android:name="com.example.MyBroadcastReceiver">
<in...
How can I reset a react component including all transitively reachable state?
...oth deprecated in the new ES6 class-style reactjs. Use this.setState(this._getInitialState()) instead. Also you can't name your own state initializer function getInitialState() - react throws a warning - call it anything else and explicitly do state = this._getInitialState() in the top level of th...
What's the advantage of a Java enum versus a class with public static final fields?
...d this 4.5 yrs ago, and at least a few people found it provided new info ¯_(ツ)_/¯
– Dave Newton
Jul 9 '17 at 17:09
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#include in .h or .c / .cpp?
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True, but doesn't the #ifndef _CALLBACK_H_, on the top of it, prevent the compiler in processing it more than once?
– hytromo
Feb 8 '14 at 12:25
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