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MySQL - length() vs char_length()
... in two bytes. Or UTF-8, where the number of bytes varies. For example:
select length(_utf8 '€'), char_length(_utf8 '€')
--> 3, 1
As you can see the Euro sign occupies 3 bytes (it's encoded as 0xE282AC in UTF-8) even though it's only one character.
...
CROSS JOIN vs INNER JOIN in SQL
...ame situation.
These 2 examples will return the same result:
Cross join
select * from table1 cross join table2 where table1.id = table2.fk_id
Inner join
select * from table1 join table2 on table1.id = table2.fk_id
Use the last method
...
Hidden Features of Java
...
Joint union in type parameter variance:
public class Baz<T extends Foo & Bar> {}
For example, if you wanted to take a parameter that's both Comparable and a Collection:
public static <A, B extends Collection<A&g...
Hidden Features of MySQL
...that has an integer type,
you can also refer to the column as "_rowid" in SELECT statements.
In MySQL, the name of a PRIMARY KEY is PRIMARY
Currently, only InnoDB (v5.1?) tables support foreign keys.
Usually, you create all the indexes you need when you are creating tables.
Any column declared...
What's the best way to join on the same table twice?
...tiple times or using subqueries etc.
I would just clean things up a bit:
SELECT t.PhoneNumber1, t.PhoneNumber2,
t1.SomeOtherFieldForPhone1, t2.someOtherFieldForPhone2
FROM Table1 t
JOIN Table2 t1 ON t1.PhoneNumber = t.PhoneNumber1
JOIN Table2 t2 ON t2.PhoneNumber = t.PhoneNumber2
What i did:...
How can I generate random alphanumeric strings?
...0123456789";
return new string(Enumerable.Repeat(chars, length)
.Select(s => s[random.Next(s.Length)]).ToArray());
}
(Note: The use of the Random class makes this unsuitable for anything security related, such as creating passwords or tokens. Use the RNGCryptoServiceProvider class if ...
Natural Sort Order in C#
...haNumeric<T>(this IEnumerable<T> source, Func<T, string> selector)
{
int max = source
.SelectMany(i => Regex.Matches(selector(i), @"\d+").Cast<Match>().Select(m => (int?)m.Value.Length))
.Max() ?? 0;
return source.OrderBy(i => Regex.Replace(s...
PHP - add item to beginning of associative array [duplicate]
...
You could use the union operator:
$arr1 = array('key0' => 'value0') + $arr1;
or array_merge.
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Select first row in each GROUP BY group?
As the title suggests, I'd like to select the first row of each set of rows grouped with a GROUP BY .
17 Answers
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Chaining multiple filter() in Django, is this a bug?
...estricted the set of blogs further to those that are also (B). The entries select by the second filter may or may not be the same as the entries in the first filter.`
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