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- $sqrt (aggregation)
$sqrt (aggregation)¶
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Definition¶
- $sqrt¶
3.2 新版功能.
Calculates the square root of a positive number and returns the result as a double.
$sqrt has the following syntax:
{ $sqrt: <number> }
The argument can be any valid expression as long as it resolves to a non-negative number. For more information on expressions, see Expressions.
Behavior¶
If the argument resolves to a value of null or refers to a field that is missing, $sqrt returns null. If the argument resolves to NaN, $sqrt returns NaN.
$sqrt errors on negative numbers.
| Example | Results |
|---|---|
| { $sqrt: 25 } | 5 |
| { $sqrt: 30 } | 5.477225575051661 |
| { $sqrt: null } | null |
Example¶
A collection points contains the following documents:
{ _id: 1, p1: { x: 5, y: 8 }, p2: { x: 0, y: 5} }
{ _id: 2, p1: { x: -2, y: 1 }, p2: { x: 1, y: 5} }
{ _id: 3, p1: { x: 4, y: 4 }, p2: { x: 4, y: 0} }
The following example uses $sqrt to calculate the distance between p1 and p2:
db.points.aggregate([
{
$project: {
distance: {
$sqrt: {
$add: [
{ $pow: [ { $subtract: [ "$p2.y", "$p1.y" ] }, 2 ] },
{ $pow: [ { $subtract: [ "$p2.x", "$p1.x" ] }, 2 ] }
]
}
}
}
}
])
The operation returns the following results:
{ "_id" : 1, "distance" : 5.830951894845301 }
{ "_id" : 2, "distance" : 5 }
{ "_id" : 3, "distance" : 4 }