mongodb distinct去重
MongoDB的destinct命令是获取特定字段中不同值列表。该命令适用于普通字段,数组字段和数组内嵌文档.
mongodb的distinct的语句:
db.users.distinct('last_name')
等同于 SQL 语句:
select DISTINCT last_name from users
表示的是根据指定的字段返回不同的记录集。
一个简单的实例:
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//
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> db.addresses.insert({"zip-code": 10010})
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> db.addresses.insert({"zip-code": 10010})
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> db.addresses.insert({"zip-code": 99701})
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> // shell helper:
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> db.addresses.distinct("zip-code");
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[ 10010, 99701 ]
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> // running as a command manually:
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> db.runCommand( { distinct: 'addresses', key: 'zip-code' } )
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{ "values" : [ 10010, 99701 ], "ok"
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//
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> db.comments.save({"user": {"points": 25}})
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> db.comments.save({"user": {"points": 31}})
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> db.comments.save({"user": {"points": 25}})
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> db.comments.distinct("user.points");
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