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使用App Inventor扩展实现多点触控：Rotation Detector · App Inventor 2 中文网
...ect two-finger rotation gestures performed on a Canvas. The demo app here, called rotationSprite, is a simple demonstration of detecting rotation gestures. You can download the apk file of the demo app from here. The demo app simply illustrates how to use the RotationDetector component to rotate a...
使用App Inventor扩展实现多点触控：Rotation Detector · App Inventor 2 中文网
...ect two-finger rotation gestures performed on a Canvas. The demo app here, called rotationSprite, is a simple demonstration of detecting rotation gestures. You can download the apk file of the demo app from here. The demo app simply illustrates how to use the RotationDetector component to rotate a...
使用App Inventor扩展实现多点触控：Rotation Detector · App Inventor 2 中文网
...ect two-finger rotation gestures performed on a Canvas. The demo app here, called rotationSprite, is a simple demonstration of detecting rotation gestures. You can download the apk file of the demo app from here. The demo app simply illustrates how to use the RotationDetector component to rotate a...
使用App Inventor扩展实现多点触控：Rotation Detector · App Inventor 2 中文网
...ect two-finger rotation gestures performed on a Canvas. The demo app here, called rotationSprite, is a simple demonstration of detecting rotation gestures. You can download the apk file of the demo app from here. The demo app simply illustrates how to use the RotationDetector component to rotate a...
CSS: fixed position on x-axis but not y?
...t;
</div>
DNA strands are composed of millions of sub-units, called nucleotides. Each nucleotide contains a 5-carbon sugar, a phosphate group and a nitrogen base. There are four different variations of the nitrogen base group, responsible for all of the variation between two different ...
ActiveRecord.find(array_of_ids), preserving order
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The answer is for mysql only
There is a function in mysql called FIELD()
Here is how you could use it in .find():
>> ids = [100, 1, 6]
=> [100, 1, 6]
>> WordDocument.find(ids).collect(&:id)
=> [1, 6, 100]
>> WordDocument.find(ids, :order => "field(id...
SQL WHERE ID IN (id1, id2, …, idn)
...ble inner join temp on temp.id = table.id
And performance improved drastically.
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How to get next/previous record in MySQL?
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All the above solutions require two database calls. The below sql code combine two sql statements into one.
select * from foo
where (
id = IFNULL((select min(id) from foo where id > 4),0)
or id = IFNULL((select max(id) from foo where id < 4),0...
What happens if you call erase() on a map element while iterating from begin to end?
...do I need to collect the keys in another container and do a second loop to call the erase()?
3 Answers
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Best way to select random rows PostgreSQL
..._pick
LIMIT _limit;
END
$func$ LANGUAGE plpgsql VOLATILE ROWS 1000;
Call:
SELECT * FROM f_random_sample();
SELECT * FROM f_random_sample(500, 1.05);
You could even make this generic to work for any table: Take the name of the PK column and the table as polymorphic type and use EXECUTE ... ...