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How to add column if not exists on PostgreSQL?
...statement:
DO $$
BEGIN
BEGIN
ALTER TABLE <table_name> ADD COLUMN <column_name> <column_type>;
EXCEPTION
WHEN duplicate_column THEN RAISE NOTICE 'column <column_name> already exists in <table_name>.';
END;
END;
$$
...
Unable to install gem - Failed to build gem native extension - cannot load such file — mkmf (LoadErr
...mitry S.Dmitry S.
89622 gold badges77 silver badges2323 bronze badges
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How can I initialize base class member variables in derived class constructor?
...ince it would destroy encapsulation. Instead, create a constructor in A to allow B (or any subclass of A) to initialize them:
class A
{
protected:
A(int a, int b) : a(a), b(b) {} // Accessible to derived classes
// Change "protected" to "public" to allow others to instantiate A.
private:
...
Generate a random double in a range
...
This is generally correct, but beware of its limits. If you do double rangeMax= Double.MAX_VALUE; and double rangeMin= -rangeMax; you will always get an infinite value in return. You might want to check for Double.valueOf(rangeMax-range...
Formatting code snippets for blogging on Blogger [closed]
... I spent a couple hours on it and I can't get this to work at all.
– thepaulpage
Mar 21 '13 at 15:43
2
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How to have the cp command create any necessary folders for copying a file to a destination [duplica
... the mkdir/cp command above. It just creates a single level of folder. Actually I'm not sure when it can be useful.
– Penghe Geng
Apr 13 '15 at 14:30
...
How to initialize a two-dimensional array in Python?
...beginning python and I'm trying to use a two-dimensional list, that I initially fill up with the same variable in every place. I came up with this:
...
Max or Default?
...wiggering the spacklerorke, and riding the flying unicorn to Neverland are all meaningless, impossible, undefined.
Now, what is it that you actually want to do?
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Mixin vs inheritance
...
A mixin is typically used with multiple inheritance. So, in that sense, there's "no difference".
The detail is that a mixin is rarely useful as a standalone object.
For example, say you have a mixin named "ColorAndDimension", which adds a co...
Assignment in an if statement
... = value as T;
if (t != null)
{
action(t);
}
}
Then call it with:
animal.AsIf<Dog>(dog => {
// Use dog in here
});
Alternatively, you could combine the two:
public static void AsIf<T>(this object value, Action<T> action) where T : class
{
// EVI...