SQL 到聚合映射图表

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• 例子

聚合管道允许 MongoDB 提供与 SQL 中许多 common 数据聚合操作相对应的本机聚合功能。

以下 table 概述了 common SQL 聚合术语，函数和概念以及相应的 MongoDB 聚合运算符：

SQL 术语，函数和概念	Mongo聚合命令
WHERE	$match
GROUP BY	$group
HAVING	$match
SELECT	$project
ORDER BY	$sort
LIMIT	$limit
SUM()	$sum
COUNT()	$sum $sortByCount
join	$lookup
SELECT INTO NEW_TABLE	$out
MERGE INTO TABLE	$merge （从MongoDB 4.2开始可用）

有关所有聚合管道和表达式 operators 的列表，请参阅聚合管道快速参考。

也可以看看

SQL 到 MongoDB 映射图表](SQL-to-Aggregation-Mapping-Chart.md)

例子

以下 table 提供了 SQL 聚合 statements 和相应的 MongoDB statements 的快速 reference。 table 中的示例假定以下条件：

• SQL 示例假设两个表orders和order_lineitem由order_lineitem.order_id和orders.id列连接。

• MongoDB 示例假设一个集合orders包含以下原型的文档：

  {
    cust_id: "abc123",
    ord_date: ISODate("2012-11-02T17:04:11.102Z"),
    status: 'A',
    price: 50,
    items: [ { sku: "xxx", qty: 25, price: 1 },
             { sku: "yyy", qty: 25, price: 1 } ]
  }

SQL语句	MongoDB语句	描述
SELECT COUNT(*) AS count FROM orders	db.orders.aggregate( [ { $group: { _id: null, count: { $sum: 1 } } } ] )	计算来自orders的所有记录
SELECT SUM(price) AS total FROM orders	db.orders.aggregate( [ { $group: { _id: null, total: { $sum: "$price" } } } ] )	orders中对price字段求和
SELECT cust_id, SUM(price) AS total FROM orders GROUP BY cust_id	db.orders.aggregate( [ { $group: { _id: "$cust_id", total: { $sum: "$price" } } } ] )	对于每个唯一cust_id，对price字段进行求和。
SELECT cust_id, SUM(price) AS total FROM orders GROUP BY cust_id ORDER BY total	db.orders.aggregate( [ { $group: { _id: "$cust_id", total: { $sum: "$price" } } }, { $sort: { total: 1 } } ] )	对于每个唯一cust_id，求和price字段，结果按总和排序。
SELECT cust_id, ord_date, SUM(price) AS total FROM orders GROUP BY cust_id, ord_date	db.orders.aggregate( [ { $group: { _id: { cust_id: "$cust_id", ord_date: { $dateToString: { format: "%Y-%m-%d", date: "$ord_date" }} }, total: { $sum: "$price" } } } ] )	对于每个唯一的cust_id，通过ord_date分组，将price字段相加。排除 data 的 time 部分。
SELECT cust_id, count(*) FROM orders GROUP BY cust_id HAVING count(*) > 1	db.orders.aggregate( [ { $group: { _id: "$cust_id", count: { $sum: 1 } } }, { $match: { count: { $gt: 1 } } } ] )	对于具有多个记录的cust_id，返回cust_id和相应的 record 计数。
SELECT cust_id, ord_date, SUM(price) AS total FROM orders GROUP BY cust_id, ord_date HAVING total > 250	db.orders.aggregate( [ { $group: { _id: { cust_id: "$cust_id", ord_date: { $dateToString: { format: "%Y-%m-%d", date: "$ord_date" }} }, total: { $sum: "$price" } } }, { $match: { total: { $gt: 250 } } } ] )	对于每个唯一的cust_id，通过ord_date分组，仅在总和大于 250 的情况下对price字段和 return 求和。排除 date 的 time 部分
SELECT cust_id, SUM(price) as total FROM orders WHERE status = 'A' GROUP BY cust_id	db.orders.aggregate( [ { $match: { status: 'A' } }, { $group: { _id: "$cust_id", total: { $sum: "$price" } } } ] )	对于状态为A的每个唯一cust_id，请对price字段求和。
SELECT cust_id, SUM(price) as total FROM orders WHERE status = 'A' GROUP BY cust_id HAVING total > 250	db.orders.aggregate( [ { $match: { status: 'A' } }, { $group: { _id: "$cust_id", total: { $sum: "$price" } } }, { $match: { total: { $gt: 250 } } } ] )	对于状态为A的每个唯一cust_id，仅对总和大于 250 的price字段和 return 求和。
SELECT cust_id, SUM(li.qty) as qty FROM orders o, order_lineitem li WHERE li.order_id = o.id GROUP BY cust_id	db.orders.aggregate( [ { $unwind: "$items" }, { $group: { _id: "$cust_id", qty: { $sum: "$items.qty" } } } ] )	对于每个唯一cust_id，将与订单关联的相应 line item qty字段相加。
SELECT COUNT(*) FROM (SELECT cust_id, ord_date FROM orders GROUP BY cust_id, ord_date) as DerivedTable	db.orders.aggregate( [ { $group: { _id: { cust_id: "$cust_id", ord_date: { $dateToString: { format: "%Y-%m-%d", date: "$ord_date" }} } } }, { $group: { _id: null, count: { $sum: 1 } } } ] )	计算不同的cust_id，ord_date分组的数量。排除 date 的 time 部分。

也可以看看

• SQL 到 MongoDB 映射图表

• 聚合管道快速参考

• db.collection.aggregate()

译者：李冠飞

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