尊龙凯时人生就是博

sqlÖÐ×óÁ´½ÓºÍÓÒÁ´½ÓÓÐʲôÇø±ð

×óÁ´½Ó±£´æ×ó±íÐУ¬ÓÒÁ´½Ó±£´æÓÒ±íÐС£×óÁ´½ÓÔÚÓÒ±íûÓÐÆ¥ÅäÐеÄ×ó±íÐÐÖÐÌî³ä null£¬¶øÓÒÁ´½ÓÔÚ×ó±íûÓÐÆ¥ÅäÐеÄÓÒ±íÐÐÖÐÌî³ä null¡£

SQL ÖÐ×óÁ´½ÓºÍÓÒÁ´½ÓµÄÇø±ð

ÔÚ SQL ÖУ¬×óÁ´½ÓºÍÓÒÁ´½Ó¶¼ÊÇÅþÁ¬±íµÄ³£ÓòÙ×÷£¬µ«ËüÃÇÔÚÊý¾Ý¼ìË÷·½·¨Éϱ£´æÏÔ×Ųî±ð¡£

×óÁ´½Ó

±£´æ×ó±íÖеÄËùÓÐÐУ¬×ÝÈ»ÓÒ±íÖÐûÓÐÆ¥ÅäµÄ¼Í¼¡£

¹ØÓÚÓÒ±íÖÐûÓÐÆ¥Åä¼Í¼µÄ×ó±íÐУ¬ÓÒ±íÁеÄÖµ½«ÏÔʾΪ NULL¡£

ÅÌÎÊÓï·¨£º

SELECT *
FROM left_table
LEFT JOIN right_table
ON left_table.key = right_table.key;

µÇ¼ºó¸´ÖÆ

ÓÒÁ´½Ó

±£´æÓÒ±íÖеÄËùÓÐÐУ¬×ÝÈ»×ó±íÖÐûÓÐÆ¥ÅäµÄ¼Í¼¡£

¹ØÓÚ×ó±íÖÐûÓÐÆ¥Åä¼Í¼µÄÓÒ±íÐУ¬×ó±íÁеÄÖµ½«ÏÔʾΪ NULL¡£

ÅÌÎÊÓï·¨£º

SELECT *
FROM right_table
RIGHT JOIN left_table
ON left_table.key = right_table.key;

µÇ¼ºó¸´ÖÆ

Ö÷ÒªÇø±ð

±£´æÐУº×óÁ´½Ó±£´æ×ó±íÐУ¬ÓÒÁ´½Ó±£´æÓÒ±íÐС£

NULL Öµ£º×óÁ´½ÓÔÚÓÒ±íûÓÐÆ¥ÅäÐеÄ×ó±íÐÐÖÐÌî³ä NULL£¬¶øÓÒÁ´½ÓÔÚ×ó±íûÓÐÆ¥ÅäÐеÄÓÒ±íÐÐÖÐÌî³ä NULL¡£

ÒÔÉϾÍÊÇsqlÖÐ×óÁ´½ÓºÍÓÒÁ´½ÓÓÐʲôÇø±ðµÄÏêϸÄÚÈÝ£¬¸ü¶àÇë¹Ø×¢±¾ÍøÄÚÆäËüÏà¹ØÎÄÕ£¡

ÃâÔð˵Ã÷£ºÒÔÉÏչʾÄÚÈÝȪԴÓÚÏàÖúýÌå¡¢ÆóÒµ»ú¹¹¡¢ÍøÓÑÌṩ»òÍøÂçÍøÂçÕûÀí£¬°æȨÕùÒéÓë±¾Õ¾Î޹أ¬ÎÄÕÂÉæ¼°¿´·¨Óë¿´·¨²»´ú±í尊龙凯时人生就是博ÂËÓÍ»úÍø¹Ù·½Ì¬¶È£¬Çë¶ÁÕß½ö×ö²Î¿¼¡£±¾ÎĽӴýתÔØ£¬×ªÔØÇë˵Ã÷À´ÓÉ¡£ÈôÄúÒÔΪ±¾ÎÄÇÖÕ¼ÁËÄúµÄ°æȨÐÅÏ¢£¬»òÄú·¢Ã÷¸ÃÄÚÈÝÓÐÈκÎÉæ¼°ÓÐÎ¥¹«µÂ¡¢Ã°·¸Ö´·¨µÈÎ¥·¨ÐÅÏ¢£¬ÇëÄúÁ¬Ã¦ÁªÏµ尊龙凯时人生就是博ʵʱÐÞÕý»òɾ³ý¡£

Ïà¹ØÐÂÎÅ

ÁªÏµ尊龙凯时人生就是博

18523999891

¿É΢ÐÅÔÚÏß×Éѯ

ÊÂÇéʱ¼ä£ºÖÜÒ»ÖÁÖÜÎ壬9:30-18:30£¬½ÚãåÈÕÐÝÏ¢

QR code
sitemap¡¢ÍøÕ¾µØͼ