sql - MySQL - SELECTing based on an IF-statement -


यदि मेरे पास फ़ील्ड एक , two कोड>, तीन और चार तब मैं किसी भी तरह फ़ील्ड चार प्राप्त करने के लिए if कथन का उपयोग कर सकता हूं, केवल तब एक निश्चित स्थिति सही है? क्या मुझे SELECT कथन के दो सेटों के पास होना है?

क्या मैं (स्यूडोकोड में) कर सकता हूँ: 

  एक, दो, तीन चुनें (1 == 1) तब तालिका से चार ईडीआईडी ​​

या मुझे कुछ करना होगा: 

  IF (1 == 1) तो एक का चयन करें

मैं बस उत्सुक हूँ, मेरे पास इस के लिए एक विशिष्ट उपयोग नहीं है।

उपयोग करें: 

  SELECT t.one, t.two, t.three, case WHEN 1 = 1 THEN टी.पूरा ELSE NULL END के रूप में चार से तालिका टी

आपके पास SELECT सूची में वैकल्पिक स्तंभ नहीं हो सकते हैं - इसमें कॉलम और एक उचित मान शामिल है , या कोई कॉलम बिल्कुल नहीं।

आप एक IF स्टेटमेंट द्वारा अलग किए गए दो (या अधिक) बयान कर सकते हैं, लेकिन किसी एक बयान में एक अतिरिक्त कॉलम के लिए आदर्श नहीं है क्योंकि आप निर्णय तर्क को आगे बढ़ा रहे हैं लापता स्तंभ स्थिति को संभालने के लिए आपका आवेदन पर।


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