database - If I have two tables in SQL with a many-many relationship, do I need to create an additional table? -

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उदाहरण के लिए इन तालिकाओं को ले जाओ। 

  आइटम आईडी वर्णन वर्ग श्रेणी आईडी वर्णन

एक आइटम कई श्रेणियों से संबंधित हो सकता है और एक श्रेणी को स्पष्ट रूप से कई वस्तुओं से जोड़ा जा सकता है।

इस स्थिति में डेटाबेस कैसे बनाया जायेगा? मुझे यकीन नहीं है। किसी ने कहा कि एक तीसरी तालिका बना, लेकिन मुझे ऐसा करने की आवश्यकता है? क्या मैं सचमुच एक

तालिका तालिका bla bla

तीसरी तालिका के लिए

हाँ, आपको आईडी की मैपिंग के साथ एक तिहाई तालिका बनाने की आवश्यकता है, कुछ ऐसे स्तंभों के साथ: 

  item_id (विदेशी कुंजी) category_id ( विदेशी कुंजी)

संपादित करें: आप item_id और category_id को प्राथमिक कुंजी के रूप में देख सकते हैं, वे अकेले रिकॉर्ड की विशिष्ट पहचान करते हैं कुछ अनुप्रयोगों में मैंने रिकॉर्ड के लिए एक अतिरिक्त संख्यात्मक पहचानकर्ता शामिल करना उपयोगी पाया है, और यदि आप ऐसा चाहते हैं तो आप वैकल्पिक रूप से एक को शामिल कर सकते हैं

इस तालिका को सभी मैपिंग की सूची के रूप में सोचें आइटम और श्रेणियाँ के बीच यह संक्षिप्त है, और इसके लिए क्वेरी करना आसान है।

संपादन: हटाया गया (अनावश्यक) प्राथमिक कुंजी।


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