紧接着上篇来，这篇主要讲，mongodb的group功能，做的还是挺强大的，相当对于find()，skip()，distinct()等，用法比较复杂。
测试数据：
><strong style="color:transparent">来源gaodaima#com搞(代@码网</strong> db.fruit.find(); { "_id" : 1, "category" : "fruit", "name" : "apple" } { "_id" : 2, "category" : "fruit", "name" : "peach" } { "_id" : 3, "category" : "fruit", "name" : "banana" } { "_id" : 4, "category" : "veggie", "name" : "corn" } { "_id" : 5, "category" : "veggie", "name" : "broccoli" }
1、根据category分组
> db.fruit.group( { key: { category: 1}, reduce: function(obj, prev) { prev.items.push(obj.name); }, initial: { items : [] } } ); [ { "category" : "fruit", "items" : [ "apple", "peach", "banana" ] }, { "category" : "veggie", "items" : [ "corn", "broccoli" ] } ]
php代码如下：
$keys = array("category" => 1); $initial = array("items" => array()); $reduce = "function (obj, prev) { prev.items.push(obj.name); }"; $g = $collection->group($keys, $initial, $reduce); print_r($g); //结果如下。 Array ( [retval] => Array ( [0] => Array ( [category] => fruit [items] => Array ( [0] => apple [1] => peach [2] => banana ) ) [1] => Array ( [category] => veggie [items] => Array ( [0] => corn [1] => broccoli ) ) ) [count] => 5 [keys] => 2 [ok] => 1 )
2、根据category来分组，并统计count
> db.fruit.group( { key: { category: 1}, cond: { _id: { $gt: 2 } }, reduce: function(obj, prev) { prev.items.push(obj.name); prev.count++; }, initial: { items : [] ,count:0} } ); [ { "category" : "fruit", "items" : [ "banana" ], "count" : 1 }, { "category" : "veggie", "items" : [ "corn", "broccoli" ], "count" : 2 } ]
php代码如下：
$keys = array("category" => 1); $initial = array("items" => array(),'count'=>0); $reduce = "function (obj, prev) { " . "prev.items.push(obj.name); " . "prev.count++;" . "}"; $condition = array('condition' => array("_id" => array( '$gt' => 2))); $g = $collection->group($keys, $initial, $reduce, $condition); print_r($g); //结果如下。 Array ( [retval] => Array ( [0] => Array ( [category] => fruit [items] => Array ( [0] => banana ) [count] => 1 ) [1] => Array ( [category] => veggie [items] => Array ( [0] => corn [1] => broccoli ) [count] => 2 ) ) [count] => 3 [keys] => 2 [ok] => 1 )
3、利用aggregate group功能，也挺强大
> db.fruit.aggregate([ { $match: { _id: {$gt:0} } }, { $group: { _id: "$category", count: { $sum: 1 } } }, { $sort: { count: -1 } } ]); { "_id" : "fruit", "count" : 3 } { "_id" : "veggie", "count" : 2 }
php代码如下：
$cond = array( array( '$match' => array('_id' => array('$gt' => 0)), ), array( '$group' => array( '_id' => '$category', 'count' => array('$sum' => 1), ), ), array( '$sort' => array("count" => -1), ), ); $result = $collection->aggregate($cond); print_r($result); //结果如下： Array ( [result] => Array ( [0] => Array ( [_id] => fruit [count] => 3 ) [1] => Array ( [_id] => veggie [count] => 2 ) ) [ok] => 1 )
mongodb 的select 操作有很多，在这里，只是说了一些常用的功能。
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