MySQL双字符主键过长 Specified key was too long; max key length is 767 bytes

Posted 2022-03-08 Silent1376

 

报错如图

 

建表SQL：

DROP TABLE IF EXISTS `pt_dict_common`;
CREATE TABLE `pt_dict_common`  (
  `DMBH` varchar(200) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT \'代码编号\',
  `DMMC` varchar(250) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT \'代码名称\',
  `DMLB` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT \'代码类别\',
  `DMLBMC` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT \'代码类别名称\',
  `SJDMBH` varchar(200) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT \'上级代码编号\',
  `TIMELINE` datetime(0) NULL DEFAULT NULL COMMENT \'时间戳\',
  `SORT` bigint(20) NULL DEFAULT NULL COMMENT \'排序\',
  PRIMARY KEY (`DMBH`, `DMLB`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = \'通用字典\' ROW_FORMAT = Dynamic;

 

问题排查定位在 声明的双主键上面：

DROP TABLE IF EXISTS `pt_dict_common`;
CREATE TABLE `pt_dict_common`  (
  `DMBH` varchar(200) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT \'代码编号\',
  `DMMC` varchar(250) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT \'代码名称\',
  `DMLB` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL COMMENT \'代码类别\',
  `DMLBMC` varchar(40) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT \'代码类别名称\',
  `SJDMBH` varchar(200) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT \'上级代码编号\',
  `TIMELINE` datetime(0) NULL DEFAULT NULL COMMENT \'时间戳\',
  `SORT` bigint(20) NULL DEFAULT NULL COMMENT \'排序\',
  PRIMARY KEY (`DMBH`, `DMLB`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci COMMENT = \'通用字典\' ROW_FORMAT = Dynamic;

默认字符双主键使用B+TREE

 

猜测是DMBH字段长度过大，在多次尝试后发现，长度设定为 191 可以创建

但是原因不知道是什么