sql - Rails group/having/count query -

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इस तरह की स्थिति को देखते हुए: कंपनी has_many उपयोगकर्ता

3 उपयोगकर्ताओं वाले कंपनियां प्राप्त करने के लिए, यह कुशलता से काम करता है: 

  कंपनी.जेंक्स (उपयोगकर्ता) .समूह ("कंपनियां.आईडी")। आईडी) = 3 ")

लेकिन 0 उपयोगकर्ता (कोई नहीं) कंपनियों को प्राप्त करने का सबसे कारगर तरीका क्या है? क्योंकि, जाहिर है, वही दृष्टिकोण काम नहीं करेगा (जैसा कि शामिल होता है परिभाषा के अनुसार 0 उपयोगकर्ता के साथ कंपनियों को शामिल नहीं करता है): 

  company.joins (users) .group (" कंपनियां.आईडी ")। (" COUNT (users.id) = 0 ")

< P> INNER JOIN की बजाय एक बाएं जुड़ें। 

  company.joins ('LEFT OUTER पर उपयोगकर्ताओं को शामिल करें users.id = users.company_id')

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