mongodb 集合操作

转自官方文档：http://docs.mongodb.org/manual/reference/sql-aggregation-comparison/

sql和mongodb集合操作对比

SQL 集合操作	MongoDB 集合操作
WHERE	$match
GROUP BY	$group
HAVING	$match
SELECT	$project
ORDER BY	$sort
LIMIT	$limit
SUM()	$sum
COUNT()	$sum
join	可以使用 $unwind实现类似操作，不过一般使用内嵌文档.

集合字段结构

{
  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 语法	MongoDB 语法
SELECT COUNT(*) AS count FROM orders	db.orders.aggregate( [{ $group: { _id: null,             count: { $sum: 1 }             }  }] )
SELECT SUM(price) AS total FROM orders	db.orders.aggregate( [{ $group: { _id: null,              total: { $sum: "$price" } }  }] )
SELECT cust_id,        SUM(price) AS total FROM orders        GROUP BY cust_id	db.orders.aggregate( [{ $group: { _id: "$cust_id",               total: { $sum: "$price" } }  }] )
SELECT cust_id,  SUM(price) AS totalF ROM orders GROUP BY cust_id ORDER BY total	db.orders.aggregate(  [   { $group: { _id: "$cust_id",                total: { $sum: "$price" } }      },     { $sort: { total: 1 } } ])
SELECT cust_id,        ord_date,        SUM(price) AS totalF ROM orders        GROUP BY cust_id, ord_date	db.orders.aggregate( [ { $group: { _id: { cust_id: "$cust_id",                      ord_date: "$ord_date"                     },              total: { $sum: "$price" } }  }] )
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: { $gt: 1 } } }] )
SELECT cust_id,        ord_date, SUM(price) AS total FROM orders GROUP BY cust_id, ord_date  HAVING total > 250	db.orders.aggregate( [{$group:{ _id:{cust_id: "$cust_id",                  ord_date: "$ord_date" },            total: { $sum: "$price" } } },   {$match: { total: { $gt: 250 } }  }] )
SELECT cust_id,   SUM(price) as total FROM orders WHERE status = 'A' GROUP BY cust_id	db.orders.aggregate( [{$match:{ status: 'A' } },  { $group:{ _id: "$cust_id",            total: { $sum: "$price" } }  }] )
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: { $gt: 250 } }   }] )
SELECT cust_id,     SUM(li.qty) as qty FROM orders o,      order_lineitem li      WHERE li.order_id = o.id      GROUP BY cust_id	db.orders.aggregate( [{$unwind: "$items" },   {$group: { _id: "$cust_id",            qty: { $sum: "$items.qty" } }   }] )
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:"$ord_date"}}},     {$group: { _id: null,             count: { $sum: 1 } }  }] )