大约有 44,000 项符合查询结果（耗时：0.0291秒） [XML]
When should I use a composite index?
...nefit a query that uses those fields for joining, filtering, and sometimes selecting. It will also benefit queries that use left-most subsets of columns in that composite. So the above index will also satisfy queries that need
index( column_A, column_B, column_C )
index( column_A, column_B )
index(...
What's the point of 'const' in the Haskell Prelude?
..., no matter the second, you can do:
listOfNothings :: String -> [Maybe Char]
listOfNothings = (map . const) Nothing
or, more explicitly:
listOfNothing st = map (const Nothing) st
share
|
imp...
C++ new int[0] — will it allocate memory?
...t be reasonable to say that a computer executing a while(!exitRequested) { char *p = new char[0]; delete [] p; } loop without recycling pointers would collapse into dust before it could possibly run out of address space, but on a platform with 32-bit pointers that would be a far less reasonable assu...
How to check if command line tools is installed
...ars in the Applications directory.
There are also the xcodebuild and xcode-select files in /usr/bin
I need to know if the command line tools is installed.
Is there a command for it?
What can I do to see if XCode CLT is installed and if yes to find the version installed?
...
Proper Repository Pattern Design in PHP?
...
public function fetch($fields)
{
return $this->db->select($fields)->from('users')->orderBy('last_name, first_name')->rows();
}
}
Before moving on to the controller, I want to show another example to illustrate how powerful this is. Maybe I have a reporting engi...
How to change options of with jQuery?
Suppose a list of options is available, how do you update the <select> with new <option> s?
9 Answers
...
Variable declaration placement in C
...declare all of your variables at the beginning of a scope block.
So, your char c declaration is valid as it is at the top of the for loop scope block. But, the char *s declaration should be an error.
share
|
...
SQL JOIN - WHERE clause vs. ON clause
...
They are not the same thing.
Consider these queries:
SELECT *
FROM Orders
LEFT JOIN OrderLines ON OrderLines.OrderID=Orders.ID
WHERE Orders.ID = 12345
and
SELECT *
FROM Orders
LEFT JOIN OrderLines ON OrderLines.OrderID=Orders.ID
AND Orders.ID = 12345
The first will re...
List of standard lengths for database fields
...ize for names in your
database. In particular, do not assume that a four-character
Japanese name in UTF-8 will fit in four bytes – you are likely to
actually need 12.
https://www.w3.org/International/questions/qa-personal-names
For database fields, VARCHAR(255) is a safe default choic...
How do I use prepared statements in SQlite in Android?
...
@jasonhudgins Why not just replace your SELECT with an INSERT? I just came from this thread, where you've confused a beginner
– keyser
May 3 '14 at 15:29
...