{"id":3989,"date":"2012-11-23T22:37:04","date_gmt":"2012-11-23T14:37:04","guid":{"rendered":"http:\/\/www.orczhou.com\/?p=3989"},"modified":"2012-11-23T22:38:14","modified_gmt":"2012-11-23T14:38:14","slug":"mysql-source-code-how-mysql-find-usable-index","status":"publish","type":"post","link":"https:\/\/www.orczhou.com\/index.php\/2012\/11\/mysql-source-code-how-mysql-find-usable-index\/","title":{"rendered":"MySQL\u6e90\u7801\uff1a\u7d22\u5f15\u76f8\u5173\u7684\u6570\u636e\u7ed3\u6784(\u540e\u7bc7)"},"content":{"rendered":"<style>\n#content h3{\n  color:red;\n  font-size:14px;\n}\n#content h4{\n  color:blue;\n  font-size:14px;\n}\n#content blockquote{\n  font-family:\"Courier New\",Courier,monospace;\n  white-space:pre;\n}\n#content h5{\n  text-indent:2em;\n}\n<\/style>\n<p>\u524d\u7bc7\u4ecb\u7ecd\u4e86MySQL\u5b58\u50a8\u7d22\u5f15\u4fe1\u606f\u7684\u57fa\u672c\u6570\u636e\u7ed3\u6784\u3002\u672c\u7bc7\u5c06\u5ef6\u7eed\u4e0b\u53bb\uff0c\u4ecb\u7ecdMySQL\u5982\u4f55\u627e\u5230\u53ef\u4ee5\u4f7f\u7528\u7684\u7d22\u5f15\uff0c\u4ee5\u53ca\u671f\u95f4\u9700\u8981\u4f7f\u7528\u7684\u4e3b\u8981\u6570\u636e\u7ed3\u6784\u3002<\/p>\n<p>\u8c01\u9002\u5408\u9605\u8bfb: \u672c\u6587\u4e0d\u6253\u7b97\u4eceHigh Level\u6765\u4ecb\u7ecdMySQL\u7d22\u5f15\u53ca\u5176\u4f7f\u7528\uff0c\u76f8\u53cd\u662f\u4eceMySQL\u6e90\u7801\u5bf9\u5e94\u7684\u6570\u636e\u7ed3\u6784\u5f00\u59cb\u4ecb\u7ecd\u3002\u5982\u679c\u4f60\u4e86\u89e3MySQL\u7d22\u5f15\u7684\u57fa\u672c\u539f\u7406\uff0c\u8fd8\u6253\u7b97\u7ee7\u7eed\u4ece\u6e90\u7801\u7684\u89d2\u5ea6\u89e3\u51b3\u4e00\u4e9b\u7d22\u5f15\u4f7f\u7528\u7684\u95ee\u9898\uff0c\u90a3\u4e48\u4f60\u9002\u5408\u53c2\u8003\u672c\u6587\uff0c\u5426\u5219\uff0c\u6253\u4f4f\uff0c\u771f\u7684\u5f88\u67af\u71e5:(\u3002\u5728\u53ef\u89c1\u7684\u672a\u6765\uff0c\u4f5c\u8005\u8fd8\u5c06\u4ecb\u7ecdRange\u4f18\u5316\u76f8\u5173\u7684\u6570\u636e\u7ed3\u6784\u7b49\u3002<\/p>\n\n<h3>0. \u6982\u8ff0<\/h3>\n<p>\u672c\u6587\u4ecb\u7ecdMySQL\u5982\u4f55\u53d1\u73b0WHERE\u6761\u4ef6\u4e2d\u7684\u7b49\u503c\u8868\u8fbe\u5f0f\uff0c\u5e76\u901a\u8fc7\u5206\u6790\u8fd9\u4e9b\u7b49\u503c\u8868\u8fbe\u5f0f\uff0c\u627e\u5230\u53ef\u4ee5\u4f7f\u7528\u7684\u7d22\u5f15\u3002\u5728\u8fd9\u4e2a\u8fc7\u7a0b\u4e2d\uff0cMySQL\u5c06\u9012\u5f52\u7684\u8bbf\u95ee\u6240\u6709WHERE\u6761\u4ef6&#8221;\u8c13\u8bcd&#8221;\uff0c\u5e76\u5c06\u7b49\u503c\u8868\u8fbe\u5f0f\u90fd\u5b58\u50a8\u5230KEY_FIELD\u5bf9\u8c61\u7684\u6570\u7ec4\u4e2d\u3002<\/p>\n<p>\u7136\u540e\u904d\u5386\u8be5KEY_FIELD\u6570\u7ec4\uff0c\u5e76\u540c\u65f6\u5bf9\u6bd4\u6240\u6709\u7d22\u5f15\u5217\uff0c\u627e\u5230\u54ea\u4e9b\u5b57\u6bb5\u662f\u5728\u7d22\u5f15\u5217\u4e2d\u51fa\u73b0\uff0c\u8fd9\u4e9b\u5b57\u6bb5\u5219\u53ef\u80fd\u53ef\u4ee5\u4f7f\u7528\u7d22\u5f15\uff0cMySQL\u5c06\u6240\u6709\u8fd9\u4e9b\u5b57\u6bb5\u90fd\u5b58\u50a8\u5728\u5bf9\u8c61KEYUSE\u6570\u7ec4\u4e2d\u3002<\/p>\n<p>\u6700\u540e\uff0c\u5bf9KEYUSE\u8fdb\u884c\u5904\u7406\uff0c\u5305\u62ec\u6392\u5e8f\u3001\u5220\u9664\u65e0\u6cd5\u4f7f\u7528\u7684\u7d22\u5f15\u5217\u3002\u8fd9\u65f6KEYUSE\u6570\u7ec4\u5c31\u662f\u6240\u6709\u53ef\u4ee5\u4f7f\u7528REF\u7684\u7d22\u5f15\u5217\u4e86\u3002<!--more--><\/p>\n<h3>1. KEY_FIELD<\/h3>\n<h4>1.1 \u6982\u8ff0<\/h4>\n<p>\u5728\u51fd\u6570JOIN::optimize\/make_join_statistics\/update_ref_and_keys\u4e2d,\u5bf9\u6240\u6709WHERE\u6761\u4ef6\u4e2d\u7684<strong>\u7b49\u503c\u8868\u8fbe\u5f0f<\/strong>\uff0c\u90fd\u8ba4\u4e3a\u53ef\u80fd\u4f1a\u8d70\u4e0a\u7d22\u5f15\uff0c\u6240\u4ee5\u90fd\u6682\u65f6\u5b58\u653e\u5230KEY_FIELD\u6570\u7ec4\u4e2d\u3002\u4f8b\u5982\u6709\u8868\u8fbe\u5f0f\uff1a&#8221;seller_id = 631389273&#8243;,\u90a3\u4e48KEY_FIELD\u6570\u7ec4\u4e2d\u5c31\u6709\u5bf9\u5e94\u7684\u5bf9\u8c61\u3002\u7ed3\u6784\u5982\u4e0b\uff1a<\/p>\n<pre><blockquote>(gdb) b add_key_part\r\nBreakpoint 2 at 0x6009e1: file sql_select.cc, line 3668.\r\n(gdb) c\r\nContinuing.\r\n\r\n(gdb) p key_field[0]\r\n$44 = {\r\n  field = 0x7f6514011728,      # \u5bf9\u5e94seller_id\u5b57\u6bb5\r\n  val = 0x7f6514005ae0,        # \u6307\u5411\u503c\u4e3a631389273\u7684Item\r\n  level = 0, \r\n  optimize = 0, \r\n  eq_func = true, \r\n  null_rejecting = false, \r\n  cond_guard = 0x0\r\n}<\/blockquote><\/pre>\n<p>MySQL\u5728\u540e\u9762\u7684\u5904\u7406\u4e2d\uff0c\u4f1a\u904d\u5386\u6240\u6709\u7684KEY_FIELD\uff0c\u5982\u679c\u53d1\u73b0\u6070\u597d\u6709\u5bf9\u5e94\u7684\u7d22\u5f15\u5728\u8fd9\u4e2a\u5b57\u6bb5\u4e0a\uff0c\u5c31\u4f1a\u5c06\u8be5\u7d22\u5f15\u6807\u8bb0\u4e3a\u53ef\u4ee5\u4f7f\u7528\u3002\u9009\u62e9\u6267\u884c\u8ba1\u5212\u7684\u65f6\u5019\uff0c\u5c31\u4f1a\u8003\u8651\u4f7f\u7528\u8fd9\u4e2a\u7d22\u5f15\u3002<\/p>\n<h4>1.2 \u5b9a\u4e49<\/h4>\n<pre><blockquote> 3065 typedef struct key_field_t {\r\n 3066   Field         *field;\r\n 3067   Item          *val;                   \/\/\/< May be empty if diff constant\r\n ......\r\n 3077 } KEY_FIELD;<\/blockquote><\/pre>\n<p>KEY_FIELD\u7684Field\u548cItem\u5b57\u6bb5\u5206\u8868\u5b58\u50a8\u4e86\u5b57\u6bb5\u548c\u5bf9\u5e94\u7684\u503c\u3002<\/p>\n<h4>1.3 KEY_FIELD\u6570\u7ec4<\/h4>\n<p>\u5047\u8bbe\u6709\u66f4\u590d\u6742\u4e00\u70b9\u7684WHERE\u6761\u4ef6\uff1a<\/p>\n<pre><blockquote>WHERE \r\n  seller_id =631389273 AND \r\n  gmt_modified = '2012-02-12 09' and \r\n  PARENT_ID=119985497951753 and \r\n  AUCTION_ID= 8932244966<\/blockquote><\/pre>\n<p>\u4e0a\u9762\u6bcf\u4e2a\u6761\u4ef6\u90fd\u4f1a\u751f\u6210\u4e00\u4e2a\u5bf9\u5e94\u7684KEY_FIELD\u5bf9\u8c61\u6765\u5b58\u50a8\uff0c\u5bf9\u5e94\u7684KEY_FIELD\u6570\u7ec4\u7ed3\u6784\u56fe\u5982\u4e0b\uff1a<\/p>\n<p><a href=\"http:\/\/www.flickr.com\/photos\/26825745@N06\/8198323275\/\" title=\"indexofkeyfield by orczhou, on Flickr\"><img loading=\"lazy\" decoding=\"async\" src=\"http:\/\/farm9.staticflickr.com\/8478\/8198323275_33f4f87d76_z.jpg\" width=\"640\" height=\"336\" alt=\"indexofkeyfield\"><\/a><\/p>\n<h3>2. MySQL\u5982\u4f55\u751f\u6210KEY_FIELD\u6570\u7ec4(\u6982\u8ff0)<\/h3>\n<p>\u5728\u51fd\u6570update_ref_and_keys\u4e2d\uff0c\u5148\u6839\u636eWHERE\u6761\u4ef6\u751f\u6210KEY_FIELD\u6570\u7ec4\uff0c\u518d\u8fdb\u4e00\u6b65\u5904\u7406\uff0c\u6700\u540e\u627e\u5230\u6240\u6709<a href=\"http:\/\/dev.mysql.com\/doc\/refman\/5.1\/en\/explain-output.html#jointype_ref\" target=\"_blank\">REF<\/a>\u53ef\u4ee5\u4f7f\u7528\u7684\u7d22\u5f15\u3002<\/p>\n<h4>2.1 update_ref_and_keys\u51fd\u6570\u7684\u4e3b\u6d41\u7a0b<\/h4>\n<pre><blockquote>\r\n(1) \u51fd\u6570\u901a\u8fc7add_key_fields\u5c06\u6240\u6709\u7684\u53ef\u80fd\u7528\u5230\u7684\u7d22\u5f15\u5b57\u6bb5\uff0c\u5168\u90e8\u90fd\u653e\u5230key_fields\u6570\u7ec4\u4e2d\r\n    (1.1) \u904d\u5386WHERE\u6811\uff0c\u9012\u5f52\u8c03\u7528add_key_fields\u3002\u5bf9\u6bcf\u4e00\u4e2aItem_func,\u8c03\u7528\u4e00\u6b21add_key_fields\r\n    (1.2) \u5bf9\u6bcf\u4e00\u4e2aItem_func(\u6709\u4e24\u4e2aItem)\uff0c\u8c03\u7528add_key_equal_fields\r\n          (1.2.1) \u4e00\u822c\u6765\u8bf4Item_func(\u5982col > 10)\uff0c\u6709\u4e24\u4e2aItem\r\n    (1.3) add_key_equal_fields\u51fd\u6570\r\n          (1.3.1)\u5c06\u8c03\u7528add_key_field\r\n                 \u8be5\u51fd\u6570\u5c06\u7b49\u503c\u6bd4\u8f83\u653e\u5230KEY_FIELD\u6570\u7ec4\u4e2d\r\n                 \u4e0d\u7b49\u503c\uff0c\u5982\u679c\u53ef\u80fd\u7528\u4e0a\u7d22\u5f15\uff0c\u5219\u5b58\u653e\u5230key_map\u5bf9\u8c61join_tab->const_keys\u4e2d\u3002\r\n                 \u8be6\u7ec6\u7684\uff1a\r\n                 {\r\n                 \u8f93\u5165\uff1aWHERE\u4e2d\u7684\u4e00\u4e2a\u5b50\u8868\u8fbe\u5f0f\uff0c\u4f8b\u5982col > 10\r\n                 \u5904\u7406\uff1a\r\n                     (1) field->key_start \u5168\u90fd\u52a0\u5165possible keys\uff1b\r\n                         \u5373\u6240\u6709\u4ee5col\u5f00\u5934\u7684\u7d22\u5f15\uff0c\u90fd\u662f\u53ef\u80fd\u7684\u7d22\u5f15\r\n                     (2) \u5982\u679cField op constant\u5219\u5c06\uff0c\u76f4\u63a5\u653e\u5230possible keys?\r\n                 \u7ed3\u679c\uff1a\r\n                     (1) key1 > 10 \u4f1a\u76f4\u63a5\u5b58\u653e\u5230possible keys\u7136\u5b58\u653e\u5b58\u653e\u5230join_tab->const_keys\r\n                     (2) key1 = 10 and key2 > 10\uff0c\u4f1a\u653e\u5230possible keys\uff0c\r\n                         \u518d\u5b58\u653e\u5230join_tab->const_keys\u3002key1\u4f1a\u5b58\u653e\u5230key_field\u6570\u7ec4\u4e2d\r\n                 }\r\n(2) \u8c03\u7528add_key_part\u5c06\u6240\u6709\u7684KEY_FIELD\u5b58\u653e\u5230\u6570\u7ec4KEYUSE\r\n(3) \u79fb\u9664KEYUSE\u6570\u7ec4\u4e2d\u65e0\u6cd5\u4f7f\u7528part\uff0c\u4f8b\u5982\u4e4b\u4f7f\u7528\u4e86\u7d22\u5f15\u7684\u7b2c\u4e8c\u4e2a\u5b57\u6bb5; \u5bf9KEYUSE\u6392\u5e8f\uff0c\r\n    \u76f8\u540c\u7684KEY\u7684\u5b57\u6bb5\u653e\u4e00\u8d77\r\n    (3.1) \u5148\u4f7f\u7528my_sort\u8fdb\u884c\u6392\u5e8f\uff1a\u6839\u636etable\/index\/keypart\u5bf9\u6240\u6709\u7684KEYUSE\u5bf9\u8c61\u8fdb\u884c\u6392\u5e8f\r\n          3986     my_qsort(keyuse->buffer,keyuse->elements,sizeof(KEYUSE),\r\n          3987           (qsort_cmp) sort_keyuse);\r\n<\/blockquote><\/pre>\n<p>(\u8fd9\u91cc\u7684(2),(3)\u6b65\u9aa4\uff0c\u5728\u672c\u7bc7\u6587\u7ae0\u540e\u90e8\u5206\u5c06\u8be6\u7ec6\u89e3\u91ca)<\/p>\n<p>\u8fd9\u4e2a\u51fd\u6570\u4f1a\u5bf9\u6240\u6709=\u6bd4\u8f83\u8868\u8fbe\u5f0f\u76f8\u5173\u7684\u8c13\u8bcd\u90fd\u653e\u5165key_fields\u5f53\u4e2d\uff0c\u7136\u540e\uff0cMySQL\u4f1a\u6839\u636e\u5404\u4e2a\u7d22\u5f15\u5b57\u6bb5\u4fe1\u606f\u751f\u6210\u5bf9\u5e94\u7684KEYUSE\u6570\u7ec4\u3002<\/p>\n<p>WHERE seller_id =631389273 AND   gmt_modified > &#8216;2012-02-12 09&#8217;\\G<br \/>\n\u8fd9\u6837\u7684WHERE\u6761\u4ef6\u4e4b\u540e\uff0c\u6211\u4eec\u770b\u5230\uff0ckey_field\u91cc\u9762\u53ea\u5b58\u50a8\u4e86\u4e00\u4e2a\u5bf9\u8c61\uff0c\u91cc\u9762\u5b58\u50a8\u7684\u662ffield\u662fSELLER_ID\u3002<\/p>\n<h4>2.2 \u51fd\u6570\u7684\u8c03\u7528\u6808<\/h4>\n<pre><blockquote>#0 add_key_field\r\n#1 add_key_fields\r\n#2 update_ref_and_keys\r\n#3  make_join_statistics \r\n#4  JOIN::optimize<\/blockquote><\/pre>\n<h3>3. KEY_FIELD\u6570\u7ec4\u8f6c\u5316\u6210KEYUSE\u5bf9\u8c61<\/h3>\n<h4>3.1 KEYUSE\u5bf9\u8c61<\/h4>\n<p>KEY_FIELD\u6570\u7ec4\u4e2d\u5305\u542b\u4e86\u6240\u6709\u7b49\u503c\u8868\u8fbe\u5f0f\u5bf9\u5e94\u5b57\u6bb5\uff0c\u4f46\u5e76\u4e0d\u662f\u6240\u6709\u8fd9\u4e9b\u5b57\u6bb5\u90fd\u6709\u5bf9\u5e94\u7684\u7d22\u5f15\u3002KEYUSE\u5bf9\u8c61\u5c31\u662f\u7528\u6765\u5b58\u50a8\u6240\u6709,\u6709\u7d22\u5f15\u7684KEY_FIELD\uff0c\u5e76\u5c06\u66f4\u591a\u7d22\u5f15\u4fe1\u606f\u5b58\u50a8\u5230KEYUSE\u4e2d\uff0c\u4ee5\u4fbf\u540e\u7eed\u4f7f\u7528\u3002\u8fd9\u4e2a\u8fc7\u7a0b\u5206\u4e24\u6b65\uff1a\u7b5b\u9009\uff1b\u6392\u5e8f\uff1b\u518d\u7b5b\u9009\u3002<\/p>\n<h5>3.1.0 \u5b9a\u4e49<\/h5>\n<pre><blockquote>(gdb) p s->keyuse[4]\r\n$90 = {\r\n table = 0x7f5bb800e980,\r\n val = 0x7f5bb8001570, \t\t# \u5b58\u50a8\u5bf9\u5e94\u7684\u503c,\u8fd9\u91cc\u662f'2012-02-12 09'\r\n used_tables = 0,\r\n key = 6,\t\t\t\t\t# \u4f7f\u7528\u7b2c6\u4e2a\u7d22\u5f15\r\n keypart = 1, \t\t\t\t# \u4ece\u96f6\u5f00\u59cb,keypart=1\u8868\u793a\u4f7f\u7528\u7684\u7b2c\u4e8c\u4e2acolumn\r\n optimize = 0,\r\n keypart_map = 2, \t\t\t# \u4e8c\u8fdb\u523611,\u4f7f\u7528\u524d\u9762\u4e24\u4e2acolumn\r\n ref_table_rows = 18446744073709551615,\r\n null_rejecting = false,\r\n cond_guard = 0x0\r\n}<\/blockquote><\/pre>\n<h5>3.1.1 \u7b5b\u9009<\/h5>\n<pre><blockquote>for ( ; field != end ; field++) #\u904d\u5386key_field\u6570\u7ec4@update_ref_and_keys\r\n{\r\n  for (uint key=0 ; key < table->keys ; key++){  #\u904d\u5386\u6240\u6709\u7d22\u5f15@add_key_part\r\n    for (uint part=0 ; part <  key_parts ; part++)  #\u904d\u5386\u7d22\u5f15\u6240\u6709\u5b57\u6bb5@add_key_part\r\n    {\r\n       if field->eq(table->key_info[key].key_part[part].field){ \r\n         #\u5982\u679c\u7d22\u5f15\u5b57\u6bb5\u8ddfkey_field\u4e2d\u7684\u5b57\u6bb5\u76f8\u540c\r\n         <\u521d\u59cb\u5316keyuse\u5bf9\u8c61>\r\n         insert_dynamic(keyuse_array,(uchar*) &keyuse)\uff1b\r\n       }\r\n    }\r\n  }\r\n}<\/blockquote><\/pre>\n<h5>3.1.2 \u6392\u5e8f<\/h5>\n<p>\u8fd9\u4e00\u6b65\u8f83\u7b80\u5355\uff0cMySQL\u4f1a\u6839\u636etable\/index\/key part\u5bf9\u6240\u6709\u7684KEYUSE\u5bf9\u8c61\u8fdb\u884c\u6392\u5e8f\uff1a<\/p>\n<pre><blockquote> 3986     my_qsort(keyuse->buffer,keyuse->elements,sizeof(KEYUSE),\r\n 3987           (qsort_cmp) sort_keyuse);<\/blockquote><\/pre>\n<p>\u8fd9\u91cc\uff0cmy_qsort\u662f\u4e00\u4e2a\u901a\u7528\u5feb\u6392\u51fd\u6570\uff0c\u6392\u5e8f\u987a\u5e8f\u5b89\u88c5\u51fd\u6570sort_keyuse\u7ed9\u51fa\uff1atablenr\u8d8a\u5927\uff0c\u503c\u8d8a\u5927\uff1b\u7d22\u5f15\u7f16\u53f7\u8d8a\u5927\uff0c\u503c\u8d8a\u5927\uff1b\u7d22\u5f15\u5217\u8d8a\u9760\u524d\uff0c\u503c\u8d8a\u5927\u3002<\/p>\n<h5>3.1.3 \u518d\u7b5b\u9009<\/h5>\n<p>\u524d\u9762\u7b5b\u9009\uff0c\u4f1a\u5c06\u6240\u6709\u5728\u7d22\u5f15\u4e2d\u7684\u5b57\u6bb5\u90fd\u653e\u5230KEYUSE\u6570\u7ec4\u4e2d\uff0c\u8fd9\u91cc\u5c06\u7ee7\u7eed\u79fb\u9664\u4ee5\u4e0b\u7684KEYUSE\u5bf9\u8c61\uff1a<\/p>\n<p>(1) \u67d0\u4e2a\u5217\u867d\u7136\u662f\u7d22\u5f15\u5217\uff0c\u4f46\u662fKEYUSE\u4e2d\u6ca1\u6709\u524d\u5bfc\u5217\u3002\u4f8b\u5982\u6709key(a,b,c)\u4f46\u6761\u4ef6\u53ea\u6709b < 5\uff0c\u5219\u79fb\u9664\u3002\n\n(2) \u5982\u679c\u6709\u7b49\u503c\u548c\u7b49\u503c\u5f15\u7528\uff0c\u5219\u79fb\u9664\u540e\u9762\u7684\u7b49\u503c\u5f15\u7528\uff0c\u5982\u6709key(a,b)\u548c\u6761\u4ef6a=3 and b=7 and b=t2.d\uff0c\u90a3\u4e48\u5c31\u4f1a\u79fb\u9664\u6761\u4ef6b=t2.d\u3002\n\n\u6761\u4ef6(1)\u5f88\u597d\u7406\u89e3\uff0cB-Tree\u7d22\u5f15\u4e0d\u80fd\u7b80\u5355\u7684\u4f7f\u7528\u8fd9\u6837\u7684\u5b57\u6bb5\u505a\u7d22\u5f15\u3002\u8fd9\u91cc\u89e3\u91ca\u4e00\u4e0b\u6761\u4ef6(2)\u3002\u770b\u5982\u4e0b\u573a\u666f\uff1a\n\n\n\n<pre><blockquote>CREATE TABLE `employee` (\r\n  `LastName` varchar(20) DEFAULT NULL,\r\n  `DepartmentID` int(11) DEFAULT NULL,\r\n  KEY `\u4ece` (`LastName`,`DepartmentID`)\r\n);\r\nCREATE TABLE `department` (\r\n  `DepartmentID` int(11) DEFAULT NULL,\r\n  `DepartmentName` varchar(20) DEFAULT NULL,\r\n  KEY `IND_D` (`DepartmentID`)\r\n)\r\n\u505a\u5982\u4e0b\u67e5\u8be2\uff1a\r\nSELECT \r\n  * \r\nFROM \r\n  employee right outer JOIN department \r\nON \r\n  employee.DepartmentID = department.DepartmentID and \r\n  employee.DepartmentID=33 and \r\n  employee.lastname = &#8216;Zhou&#8217;\r\n<\/blockquote><\/pre>\n<p>\u56e0\u4e3aright join\uff0c\u6240\u4ee5department\u987a\u5e8f\u603b\u662f\u5728\u524d\u3002MySQL\u5728\u8003\u5bdfemployee\u8868\u53ef\u4ee5\u8d70\u54ea\u4e9b\u7d22\u5f15\u7684\u65f6\u5019\uff0c\u5148\u6536\u96c6\u5230\u4e09\u4e2aKEY_FIELD\u7b49\u503c\u8868\u8fbe\u5f0f\uff0c\u56e0\u4e3a\u7d22\u5f15IND_L_D\u5305\u542b\u4e86\u8fd9\u4e24\u4e2a\u5b57\u6bb5\uff0c\u6240\u4ee5\u8fd9\u4e09\u4e2a\u7b49\u503c\u8868\u8fbe\u5f0f\u90fd\u4f1a\u5b58\u50a8\u5230KEYUSE\u6570\u7ec4\u4e2d\u3002\u800c\u4e09\u4e2aKEYUSE\u5728\u6570\u7ec4\u7684\u4e2d\u7684\u987a\u5e8f\u5982\u4e0b\uff1a<\/p>\n<p>KEYUSE(lastname,&#8217;Zhou&#8217;),KEYUSE(DepartmentID,33),KEYUSE(DepartmentID,department.DepartmentID)<\/p>\n<p>\u8fd9\u91cc\u7684\u7b2c\u4e09\u4e2a\u7b49\u5f0f\uff0c\u662f\u4e00\u4e2a\u5f15\u7528\uff0c\u4f46\u662femployee\u662f\u8fde\u63a5\u7684\u5916\u90e8\u8868\uff0c\u6240\u4ee5\u5728\u626b\u63cfemployee\u65f6\uff0c\u5c06\u5ffd\u7565\u7b2c\u4e09\u4e2a\u6761\u4ef6\uff0c\u5bf9\u5e94\u7684KEYUSE\u5c06\u5220\u9664\u8fd9\u4e2a\u6761\u4ef6\u3002<\/p>\n<p>\u66f4\u591a\u89e3\u91ca\u548c\u7591\u95ee\uff1a(1) KEYUSE\u6392\u5e8f\u4f1a\u5c06\u5e38\u6570\u653e\u5728\u524d\u9762 (2) \u4e00\u4e2a\u7591\u95ee\uff0cON\u6761\u4ef6\u4e2d\u7684employee.lastname = &#8216;Zhou&#8217;\uff0c\u653e\u5728ON\u91cc\u9762\u548c\u653e\u5728WHERE\u91cc\u9762\u6709\u4ec0\u4e48\u533a\u522b?<\/p>\n<h4>3.2 \u5b8c\u6574\u7684KEYUSE\u6570\u7ec4<\/h4>\n<pre><blockquote>                                        \r\n                                    |-> p s->keyuse[1]\r\n          |-->keyuse[0]  [KEYUSE]   |->   { table = 0x7f5bb800e980, \r\nINDEX[1]->|-->keyuse[1] ----------> |->     ...\r\n          |-->keyuse[2]             |->     key = 1,           #\u4f7f\u7528\u7b2c\u4e00\u4e2a\u7d22\u5f15\r\n                                    |->     keypart = 1,       #\u4ece\u96f6\u5f00\u59cb,1\u8868\u793a\u4f7f\u7528\u7684\u7b2c\u4e8c\u4e2acolumn\r\n          |-->keyuse[3]             |->     keypart_map = 2,   #\u4e8c\u8fdb\u523611,\u4f7f\u7528\u524d\u9762\u4e24\u4e2acolumn\r\nINDEX[3]->|                         |->     ...\r\n          |-->keyuse[4]             |->   }\r\n<\/blockquote><\/pre>\n<p>\u672c\u7bc7\u5c31\u4ecb\u7ecd\u5230\u6b64\uff0c\u540e\u9762\u5c06\u6839\u636e\u8fd9\u4e9b\u7ed3\u6784\uff0c\u770b\u770bMySQL\u5982\u4f55\u5982\u4f55\u6839\u636e\u8fd9\u4e9b\u7ed3\u6784\u9009\u62e9\u6267\u884c\u8ba1\u5212\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u524d\u7bc7\u4ecb\u7ecd\u4e86MySQL\u5b58\u50a8\u7d22\u5f15\u4fe1\u606f\u7684\u57fa\u672c\u6570\u636e\u7ed3\u6784\u3002\u672c\u7bc7\u5c06\u5ef6\u7eed\u4e0b\u53bb\uff0c\u4ecb\u7ecdMySQL\u5982\u4f55\u627e\u5230\u53ef\u4ee5\u4f7f\u7528\u7684\u7d22\u5f15\uff0c\u4ee5\u53ca\u671f\u95f4\u9700\u8981\u4f7f\u7528\u7684\u4e3b\u8981\u6570\u636e\u7ed3\u6784\u3002 \u8c01\u9002\u5408\u9605\u8bfb: \u672c\u6587\u4e0d\u6253\u7b97\u4eceHigh Level\u6765\u4ecb\u7ecdMySQL\u7d22\u5f15\u53ca\u5176\u4f7f\u7528\uff0c\u76f8\u53cd\u662f\u4eceMySQL\u6e90\u7801\u5bf9\u5e94\u7684\u6570\u636e\u7ed3\u6784\u5f00\u59cb\u4ecb\u7ecd\u3002\u5982\u679c\u4f60\u4e86\u89e3MySQL\u7d22\u5f15\u7684\u57fa\u672c\u539f\u7406\uff0c\u8fd8\u6253\u7b97\u7ee7\u7eed\u4ece\u6e90\u7801\u7684\u89d2\u5ea6\u89e3\u51b3\u4e00\u4e9b\u7d22\u5f15\u4f7f\u7528\u7684\u95ee\u9898\uff0c\u90a3\u4e48\u4f60\u9002\u5408\u53c2\u8003\u672c\u6587\uff0c\u5426\u5219\uff0c\u6253\u4f4f\uff0c\u771f\u7684\u5f88\u67af\u71e5:(\u3002\u5728\u53ef\u89c1\u7684\u672a\u6765\uff0c\u4f5c\u8005\u8fd8\u5c06\u4ecb\u7ecdRange\u4f18\u5316\u76f8\u5173\u7684\u6570\u636e\u7ed3\u6784\u7b49\u3002 0. \u6982\u8ff0 \u672c\u6587\u4ecb\u7ecdMySQL\u5982\u4f55\u53d1\u73b0WHERE\u6761\u4ef6\u4e2d\u7684\u7b49\u503c\u8868\u8fbe\u5f0f\uff0c\u5e76\u901a\u8fc7\u5206\u6790\u8fd9\u4e9b\u7b49\u503c\u8868\u8fbe\u5f0f\uff0c\u627e\u5230\u53ef\u4ee5\u4f7f\u7528\u7684\u7d22\u5f15\u3002\u5728\u8fd9\u4e2a\u8fc7\u7a0b\u4e2d\uff0cMySQL\u5c06\u9012\u5f52\u7684\u8bbf\u95ee\u6240\u6709WHERE\u6761\u4ef6&#8221;\u8c13\u8bcd&#8221;\uff0c\u5e76\u5c06\u7b49\u503c\u8868\u8fbe\u5f0f\u90fd\u5b58\u50a8\u5230KEY_FIELD\u5bf9\u8c61\u7684\u6570\u7ec4\u4e2d\u3002 \u7136\u540e\u904d\u5386\u8be5KEY_FIELD\u6570\u7ec4\uff0c\u5e76\u540c\u65f6\u5bf9\u6bd4\u6240\u6709\u7d22\u5f15\u5217\uff0c\u627e\u5230\u54ea\u4e9b\u5b57\u6bb5\u662f\u5728\u7d22\u5f15\u5217\u4e2d\u51fa\u73b0\uff0c\u8fd9\u4e9b\u5b57\u6bb5\u5219\u53ef\u80fd\u53ef\u4ee5\u4f7f\u7528\u7d22\u5f15\uff0cMySQL\u5c06\u6240\u6709\u8fd9\u4e9b\u5b57\u6bb5\u90fd\u5b58\u50a8\u5728\u5bf9\u8c61KEYUSE\u6570\u7ec4\u4e2d\u3002 \u6700\u540e\uff0c\u5bf9KEYUSE\u8fdb\u884c\u5904\u7406\uff0c\u5305\u62ec\u6392\u5e8f\u3001\u5220\u9664\u65e0\u6cd5\u4f7f\u7528\u7684\u7d22\u5f15\u5217\u3002\u8fd9\u65f6KEYUSE\u6570\u7ec4\u5c31\u662f\u6240\u6709\u53ef\u4ee5\u4f7f\u7528REF\u7684\u7d22\u5f15\u5217\u4e86\u3002<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_eb_attr":"","inline_featured_image":false,"_tocer_settings":[],"footnotes":""},"categories":[6,5],"tags":[101,118,58],"class_list":["post-3989","post","type-post","status-publish","format-standard","hentry","category-mysql","category-code-staff","tag-index","tag-mysql","tag-source-code"],"_links":{"self":[{"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/posts\/3989","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/comments?post=3989"}],"version-history":[{"count":38,"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/posts\/3989\/revisions"}],"predecessor-version":[{"id":4109,"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/posts\/3989\/revisions\/4109"}],"wp:attachment":[{"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/media?parent=3989"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/categories?post=3989"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.orczhou.com\/index.php\/wp-json\/wp\/v2\/tags?post=3989"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}