database - postgres: constraint check and null values -

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कृपया निम्न तालिका पर एक नज़र डालें: 

  नाम | एक्स | Y --------- + ----- + ------ foo | 3 | 5 बार | 45 | 99 फ़ॉउबर | 88 | बारफू | 0 | 45

मैं एक बाधा जांच (y> x) जोड़ना चाहता हूं, लेकिन यह स्पष्ट रूप से असफल हो जायेगी क्योंकि इसका उल्लंघन 'फोबार' द्वारा किया जाता है।

कैसे करें मैं कहता है कि एक बाधा उत्पन्न करता है: चेक (y> x), लेकिन तभी यदि y नल हो?

वास्तव में, आपको वास्तव में कुछ और करने की ज़रूरत नहीं है एक चेक बाधा संतुष्ट है यदि चेक अभिव्यक्ति सही या शून्य मान का मूल्यांकन करती है।

आपकी बाधा जांच (वाई> एक्स) आपके परिदृश्य में काम करेगी क्योंकि पंक्ति फ़ोबार बाधा का उल्लंघन नहीं करेगा रिक्त करने के लिए मूल्यांकन


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