gistfile1.txt

first inserting documents like:

db.businesses.insert({tags: ['A']})


businesses@sam-HP-Z400> db.businesses.getIndexes()
[
	{
		"v" : 1,
		"key" : {
			"_id" : 1
		},
		"ns" : "businesses.businesses",
		"name" : "_id_"
	},
	{
		"v" : 1,
		"key" : {
			"tags" : 1
		},
		"ns" : "businesses.businesses",
		"name" : "tags_1"
	}
]




businesses@sam-HP-Z400> db.businesses.find({$and: [{tags: {$in: ['A']}}, {tags: {$in: ['C']}}]}).explain()
{
	"cursor" : "BtreeCursor tags_1",
	"isMultiKey" : true,
	"n" : 88,
	"nscannedObjects" : 235,
	"nscanned" : 235,
	"nscannedObjectsAllPlans" : 235,
	"nscannedAllPlans" : 235,
	"scanAndOrder" : false,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 0,
	"indexBounds" : {
		"tags" : [
			[
				"A",
				"A"
			]
		]
	},
	"server" : "sam-HP-Z400:27017"
}




businesses@sam-HP-Z400> db.businesses.find({tags: ['C', 'A']}).explain()
{
	"cursor" : "BtreeCursor tags_1 multi",
	"isMultiKey" : true,
	"n" : 0,
	"nscannedObjects" : 88,
	"nscanned" : 89,
	"nscannedObjectsAllPlans" : 88,
	"nscannedAllPlans" : 89,
	"scanAndOrder" : false,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 0,
	"indexBounds" : {
		"tags" : [
			[
				"C",
				"C"
			],
			[
				[
					"C",
					"A"
				],
				[
					"C",
					"A"
				]
			]
		]
	},
	"server" : "sam-HP-Z400:27017"
}






businesses@sam-HP-Z400> db.businesses.find({$and: [{tags: {$in: ['C']}}, {tags: {$in: ['A']}}]}).explain()
{
	"cursor" : "BtreeCursor tags_1",
	"isMultiKey" : true,
	"n" : 88,
	"nscannedObjects" : 88,
	"nscanned" : 88,
	"nscannedObjectsAllPlans" : 88,
	"nscannedAllPlans" : 88,
	"scanAndOrder" : false,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 0,
	"indexBounds" : {
		"tags" : [
			[
				"C",
				"C"
			]
		]
	},
	"server" : "sam-HP-Z400:27017"
}




then insert documents like:
db.businesses.insert({tags: {'A':1}})

businesses@sam-HP-Z400> db.businesses.find({tags: {$all: ['A', 'C']}}).explain()
{
	"cursor" : "BtreeCursor tags_1",
	"isMultiKey" : true,
	"n" : 0,
	"nscannedObjects" : 0,
	"nscanned" : 0,
	"nscannedObjectsAllPlans" : 0,
	"nscannedAllPlans" : 0,
	"scanAndOrder" : false,
	"indexOnly" : false,
	"nYields" : 0,
	"nChunkSkips" : 0,
	"millis" : 0,
	"indexBounds" : {
		"tags" : [
			[
				"A",
				"A"
			]
		]
	},
	"server" : "sam-HP-Z400:27017"
}