Details
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Task
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Resolution: Duplicate
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Major - P3
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None
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None
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None
Description
Engineering Ticket Description:
Syntax
{
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$bucket: {
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groupBy: <arbitrary expression>,
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boundaries: [
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// Array of constant values. |
],
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default: <constant expression>, |
output: { // Still optional, defaults to {count: {$sum: 1}} |
fieldName1: <accumulator 1>,
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fieldName2: <accumulator 2>
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}
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}
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}
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Examples
> db.example.insert([
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{_id: 0, screenSize: 30},
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{_id: 1, screenSize: 24},
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{_id: 2, screenSize: 42},
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{_id: 3, screenSize: 22},
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{_id: 4, screenSize: 55},
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]);
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> db.example.aggregate([
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{
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$bucket: {
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groupBy: "$screenSize", |
boundaries: [0, 24, 32, 50, Infinity], // Makes 4 buckets, the _id is based on the min: |
// [0, 24), [24, 32), [32, 50), [50, Infinity) |
default: "other", |
output: {
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count: {$sum: 1},
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matches: {$push: "$screenSize"} |
}
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}
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}
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])
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{_id: 0, count: 1, matches: [22]}
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{_id: 24, count: 2, matches: [24, 30]}
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{_id: 32, count: 1, matches: [42]}
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{_id: 50, count: 1, matches: [55]}
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{_id: "other", count: 2, matches: [null, "not-a-number"]} |
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// ===================== Example #2 - Error on unexpected types ==========================
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> db.example.insert([
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{_id: 0, screenSize: 30},
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{_id: 1, screenSize: 24},
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{_id: 2, screenSize: 42},
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{_id: 3, screenSize: 22},
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{_id: 4, screenSize: 55},
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{_id: 5, screenSize: "not-a-number"}, |
{_id: 6, screenSize: null}, |
]);
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> db.example.aggregate([
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{
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$bucket: {
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groupBy: "$screenSize", |
boundaries: [0, 24, 32, 50, Infinity],
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// No default specified. |
}
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}
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])
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Error!
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// ===================== Example #3 - Group unexpected types together =====================
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> db.example.insert([
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{_id: 0, screenSize: 30},
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{_id: 1, screenSize: 24},
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{_id: 2, screenSize: 42},
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{_id: 3, screenSize: 22},
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{_id: 4, screenSize: 55},
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{_id: 5, screenSize: "not-a-number"}, |
{_id: 6, screenSize: null}, |
]);
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> db.example.aggregate([
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{
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$bucket: {
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groupBy: "$screenSize", |
boundaries: [0, 24, 32, 50, Infinity],
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default: "other", |
output: {
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count: {$sum: 1},
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matches: {$push: "$screenSize"} |
}
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}
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}
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])
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{_id: 0, count: 1, matches: [22]}
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{_id: 24, count: 2, matches: [24, 30]}
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{_id: 32, count: 1, matches: [42]}
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{_id: 50, count: 1, matches: [55]}
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{_id: "other", count: 2, matches: [null, "not-a-number"]} |
Detailed Behavior
- This stage is very similar to the following:
{$group: {_id: <some sort of $switch expression on the 'groupBy' to put it into buckets based on 'boundaries'>,
fieldName1: <accumulator 1>fieldName2: <accumulator 2>}} - 'boundaries' must be constant values (can't use "$x", but can use {$add: [4, 5]}), and must be sorted.
- Output documents will be sorted (in the order entered).
- Values that are equal to a boundary will go into the range with that boundary as the minimum.
- For example, with boundaries [0, 2, 4], 2 would go into the bucket with an _id of 2, which would encompass the range [2, 4)
- The only expected use cases are numeric values and date-like types, but we'll support arbitrary values.
- This will have to follow the operation's collation when comparing strings.
- There is no way to assign labels to the buckets, the _id of the output document will be the minimum value for that bucket's range.
Attachments
Issue Links
- documents
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SERVER-23815 Add $bucket aggregation stage
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- Closed
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