{"id":7708,"date":"2024-11-14T14:19:10","date_gmt":"2024-11-14T06:19:10","guid":{"rendered":"https:\/\/fwq.ai\/blog\/7708\/"},"modified":"2024-11-14T14:19:10","modified_gmt":"2024-11-14T06:19:10","slug":"mysql-%e4%b8%ad%e7%9a%84-key_len-%e4%b8%ba%e4%bb%80%e4%b9%88%e4%bc%9a%e5%a4%a7%e4%ba%8e%e7%b4%a2%e5%bc%95%e5%88%97%e7%9a%84%e9%95%bf%e5%ba%a6%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/fwq.ai\/blog\/7708\/","title":{"rendered":"MySQL \u4e2d\u7684 key_len \u4e3a\u4ec0\u4e48\u4f1a\u5927\u4e8e\u7d22\u5f15\u5217\u7684\u957f\u5ea6\uff1f"},"content":{"rendered":"

\"MySQL<\/p>\n

MySQL\uff1a\u5173\u4e8e key_len \u8ba1\u7b97\u65b9\u5f0f\u7684\u89e3\u6790<\/strong><\/p>\n

\u95ee\u9898\u63cf\u8ff0\uff1a<\/strong><\/p>\n

\u5728 MySQL 8.0.18 \u4e2d\uff0c\u521b\u5efa\u4e86\u4e00\u4e2a\u8868 student\uff0c\u5176\u4e2d\u5305\u542b\u4e00\u4e2a char(20) \u7684\u5217 student_name\uff0c\u5e76\u5efa\u7acb\u4e86\u7d22\u5f15 student_name_index\u3002\u5411\u8868\u4e2d\u63d2\u5165\u4e86\u4e09\u6761\u6570\u636e\u3002<\/p>\n

\u901a\u8fc7\u4f7f\u7528 EXPLAIN \u67e5\u770b\u6267\u884c\u8ba1\u5212\uff0c\u53d1\u73b0\u6700\u7ec8\u4f7f\u7528\u7684\u7d22\u5f15\u7684 key_len \u4e3a 80\u3002\u7136\u800c\uff0c\u8868\u4e2d\u53ea\u6709\u4e09\u6761\u8bb0\u5f55\uff0ckey_len \u5e94\u8be5\u4e3a20 * 3 = 60\uff0c\u4e3a\u4f55\u51fa\u73b0\u8fd9\u79cd\u60c5\u51b5\uff1f<\/p>\n

\u7b54\u6848\u89e3\u6790\uff1a<\/strong><\/p>\n

char(20) \u5b9a\u4e49\u4e86\u4e00\u4e2a\u5b9a\u957f\u5b57\u7b26\u7c7b\u578b\uff0c\u53ef\u4ee5\u5b58\u50a8\u957f\u5ea6\u4e0d\u8d85\u8fc7 20 \u4e2a\u5b57\u8282\u7684\u5b57\u7b26\u4e32\u3002\u800c utf8mb4 \u662f\u4e00\u79cd\u7f16\u7801\u65b9\u5f0f\uff0c\u5b83\u5141\u8bb8\u4f7f\u7528\u4e0d\u540c\u7684\u5b57\u8282\u6570\u6765\u8868\u793a\u4e0d\u540c\u7684\u5b57\u7b26\u3002\u5bf9\u4e8e utf8mb4 \u7f16\u7801\uff0c\u4e00\u4e2a\u5b57\u7b26\u6700\u591a\u53ef\u4ee5\u5360 4 \u4e2a\u5b57\u8282\u3002<\/p>\n

\u56e0\u6b64\uff0c\u5bf9\u4e8e student_name \u5217\uff0c\u5176\u957f\u5ea6\u4e3a 20 \u4e2a\u5b57\u7b26\uff0c\u4f46\u7531\u4e8e\u4f7f\u7528\u7684\u662f utf8mb4 \u7f16\u7801\uff0c\u6bcf\u4e2a\u5b57\u7b26\u5b9e\u9645\u5360\u7528 4 \u4e2a\u5b57\u8282\uff0c\u6240\u4ee5 key_len \u5b9e\u9645\u4e0a\u4e3a 20 * 4 = 80\u3002<\/p>\n

\u4e0e\u8868\u4e2d\u8bb0\u5f55\u7684\u6570\u91cf\u65e0\u5173\uff0ckey_len \u59cb\u7ec8\u662f\u7d22\u5f15\u5217\u5b9e\u9645\u5360\u7528\u7684\u5b57\u8282\u6570\u3002<\/p>\n

\u4ee5\u4e0a\u5c31\u662fMySQL \u4e2d\u7684 key_len \u4f1a\u5927\u4e8e\u7d22\u5f15\u5217\u7684\u957f\u5ea6\uff1f\u7684\u8be6\u7ec6\u5185\u5bb9\uff0c\u66f4\u591a\u8bf7\u5173\u6ce8\u7c73\u4e91\u7f51\u5176\u5b83\u76f8\u5173\u6587\u7ae0\uff01<\/p>\n","protected":false},"excerpt":{"rendered":"

MySQL\uff1a\u5173\u4e8e key_len \u8ba1\u7b97\u65b9\u5f0f\u7684\u89e3\u6790 \u95ee\u9898\u63cf\u8ff0\uff1a \u5728 MySQL 8.0.18 \u4e2d\uff0c\u521b\u5efa\u4e86\u4e00\u4e2a\u8868 student\uff0c\u5176\u4e2d\u5305\u542b\u4e00\u4e2a char(20) \u7684\u5217 student_name\uff0c\u5e76\u5efa\u7acb\u4e86\u7d22\u5f15 student_name_index\u3002\u5411\u8868\u4e2d\u63d2\u5165\u4e86\u4e09\u6761\u6570\u636e\u3002 \u901a\u8fc7\u4f7f\u7528 EXPLAIN \u67e5\u770b\u6267\u884c\u8ba1\u5212\uff0c\u53d1\u73b0\u6700\u7ec8\u4f7f\u7528\u7684\u7d22\u5f15\u7684 key_len \u4e3a 80\u3002\u7136\u800c\uff0c\u8868\u4e2d\u53ea\u6709\u4e09\u6761\u8bb0\u5f55\uff0ckey_len \u5e94\u8be5\u4e3a20 * 3 = 60\uff0c\u4e3a\u4f55\u51fa\u73b0\u8fd9\u79cd\u60c5\u51b5\uff1f \u7b54\u6848\u89e3\u6790\uff1a char(20) \u5b9a\u4e49\u4e86\u4e00\u4e2a\u5b9a\u957f\u5b57\u7b26\u7c7b\u578b\uff0c\u53ef\u4ee5\u5b58\u50a8\u957f\u5ea6\u4e0d\u8d85\u8fc7 20 \u4e2a\u5b57\u8282\u7684\u5b57\u7b26\u4e32\u3002\u800c utf8mb4 \u662f\u4e00\u79cd\u7f16\u7801\u65b9\u5f0f\uff0c\u5b83\u5141\u8bb8\u4f7f\u7528\u4e0d\u540c\u7684\u5b57\u8282\u6570\u6765\u8868\u793a\u4e0d\u540c\u7684\u5b57\u7b26\u3002\u5bf9\u4e8e utf8mb4 \u7f16\u7801\uff0c\u4e00\u4e2a\u5b57\u7b26\u6700\u591a\u53ef\u4ee5\u5360 4 \u4e2a\u5b57\u8282\u3002 \u56e0\u6b64\uff0c\u5bf9\u4e8e student_name \u5217\uff0c\u5176\u957f\u5ea6\u4e3a 20 \u4e2a\u5b57\u7b26\uff0c\u4f46\u7531\u4e8e\u4f7f\u7528\u7684\u662f utf8mb4 \u7f16\u7801\uff0c\u6bcf\u4e2a\u5b57\u7b26\u5b9e\u9645\u5360\u7528 4 \u4e2a\u5b57\u8282\uff0c\u6240\u4ee5 key_len \u5b9e\u9645\u4e0a\u4e3a 20 * 4 = 80\u3002 \u4e0e\u8868\u4e2d\u8bb0\u5f55\u7684\u6570\u91cf\u65e0\u5173\uff0ckey_len \u59cb\u7ec8\u662f\u7d22\u5f15\u5217\u5b9e\u9645\u5360\u7528\u7684\u5b57\u8282\u6570\u3002 \u4ee5\u4e0a\u5c31\u662fMySQL \u4e2d\u7684 […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[16],"tags":[],"class_list":["post-7708","post","type-post","status-publish","format-standard","hentry","category-16"],"_links":{"self":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/7708","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/comments?post=7708"}],"version-history":[{"count":0,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/posts\/7708\/revisions"}],"wp:attachment":[{"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/media?parent=7708"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/categories?post=7708"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/fwq.ai\/blog\/wp-json\/wp\/v2\/tags?post=7708"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}