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Computed / calculated / virtual / derived columns in PostgreSQL
...l, but makes makes life a bit easier).
Suppose my computation is md5(some_string_field), then I create the index as:
CREATE INDEX some_string_field_md5_index ON some_table(MD5(some_string_field));
Now, any queries that act on MD5(some_string_field) will use the index rather than computing it fr...
KeyValuePair VS DictionaryEntry
...expand on Chris' example (in which we have two dictionaries containing <string, int> pairs).
Dictionary<string, int> dict = new Dictionary<string, int>();
foreach (KeyValuePair<string, int> item in dict) {
int i = item.Value;
}
Hashtable hashtable = new Hashtable();
forea...
Differences between Perl and PHP [closed]
...uding matching (=~, !~), quote-like (qw, qx &c.), exponentiation (**), string repetition (x) and range (.. and ...). PHP has a few operators Perl doesn't, such as the error suppression operator (@), instanceof (though Perl does have the Universal::isa method) and clone.
In PHP, new is an operat...
What is the difference between single and double quotes in SQL?
...
Single quotes are used to indicate the beginning and end of a string in SQL. Double quotes generally aren't used in SQL, but that can vary from database to database.
Stick to using single quotes.
That's the primary use anyway. You can use single quotes for a column alias — where yo...
How to store a command in a variable in a shell script?
...ning about the risk of unexpected parsing behavior (even without malicious strings, as in @CharlesDuffy's example). For example, try x='echo $(( 6 * 7 ))' and then eval $x. You might expect that to print "42", but it probably won't. Can you explain why it doesn't work? Can you explain why I said "pr...
Android Paint: .measureText() vs .getTextBounds()
...hat measureText calls native_measureText, and getTextBounds calls nativeGetStringBounds, which are native methods implemented in C++.
So you'd continue to study Paint.cpp, which implements both.
native_measureText -> SkPaintGlue::measureText_CII
nativeGetStringBounds -> SkPaintGlue::getStri...
Setting environment variables on OS X
...;plist version="1.0">
<dict>
<key>Label</key>
<string>osx-env-sync</string>
<key>ProgramArguments</key>
<array>
<string>bash</string>
<string>-l</string>
<string>-c</string>
<string>
...
Is there an MD5 Fixed Point where md5(x) == x?
...cessarily also have to be 128 bits long. Assuming that the MD5 sum of any string is uniformly distributed over all possible sums, then the probability that any given 128-bit string is a fixed point is 1/2128.
Thus, the probability that no 128-bit string is a fixed point is (1 − 1/2128)2128, so t...
How to get datetime in JavaScript?
...emantically, you're probably looking for the one-liner
new Date().toLocaleString()
which formats the date in the locale of the user.
If you're really looking for a specific way to format dates, I recommend the moment.js library.
...
String formatting in Python 3
... old format syntax nor in the new, thus should be present in the generated string, unchanged.
– mgibsonbr
Mar 22 '19 at 5:45
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