Mysql唯一索引线上故障记录

Posted 2021-03-18 后青春期的Keats

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问题现象：

Mysql插入一条数据时，未指定自增键的值却报错：自增键重复，无法插入！

执行SQL

INSERT INTO `test`.`test_sort`(`id`, `name`, `age`, `birthday`) VALUES 
(10027, \'测试\', 23, \'2020-01-07 12:23:11\')

报错：

INSERT INTO `test`.`test_sort`(`id`, `name`, `age`, `birthday`) VALUES 
(10027, \'测试\', 23, \'2020-01-07 12:23:11\')
> 1062 - Duplicate entry \'38\' for key \'sort\'
> 时间: 0.001s

表的创建语句：

CREATE TABLE `test_sort`  (
  `id` int(11) NOT NULL COMMENT \'主键\',
  `name` varchar(24) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NULL DEFAULT NULL COMMENT \'姓名\',
  `age` tinyint(3) UNSIGNED NULL DEFAULT NULL COMMENT \'年龄\',
  `birthday` datetime(0) NULL DEFAULT NULL COMMENT \'生日\',
  `sort` int(11) NOT NULL AUTO_INCREMENT COMMENT \'序号\',
  PRIMARY KEY (`id`) USING BTREE,
  UNIQUE INDEX `sort`(`sort`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 39 CHARACTER SET = latin1 COLLATE = latin1_swedish_ci ROW_FORMAT = Dynamic;

这里可以发现，sort字段在表中是自增键，通过唯一索引 sort 来实现，而我在插入新行的时候没有指定 sort 字段的值，那么它理论上会采用当前自增 B-Tree 上最大数字 + 1，这里却提示他冲突了。

问题还原

表里面原来的数据如下：

INSERT INTO `test_sort` VALUES (10001, \'张三\', 23, \'2020-01-07 12:23:11\', 1);
INSERT INTO `test_sort` VALUES (10002, \'王五\', 23, \'2020-01-07 12:23:11\', 9);
INSERT INTO `test_sort` VALUES (10003, \'赵六\', 23, \'2020-01-07 12:23:11\', 10);
INSERT INTO `test_sort` VALUES (10004, \'钱七\', 23, \'2020-01-07 12:23:11\', 11);
INSERT INTO `test_sort` VALUES (10005, \'刘八\', 23, \'2020-01-07 12:23:11\', 12);
INSERT INTO `test_sort` VALUES (10006, \'冯九\', 23, \'2020-01-07 12:23:11\', 13);
INSERT INTO `test_sort` VALUES (10007, \'李四\', 23, \'2020-01-07 12:23:11\', 44);
INSERT INTO `test_sort` VALUES (10008, \'李四1\', 23, \'2020-01-07 12:23:11\', 36);
INSERT INTO `test_sort` VALUES (10009, \'王五1\', 23, \'2020-01-07 12:23:11\', 38);
INSERT INTO `test_sort` VALUES (10010, \'赵六1\', 23, \'2020-01-07 12:23:11\', 40);
INSERT INTO `test_sort` VALUES (10011, \'钱七1\', 23, \'2020-01-07 12:23:11\', 41);
INSERT INTO `test_sort` VALUES (10012, \'刘八1\', 23, \'2020-01-07 12:23:11\', 46);
INSERT INTO `test_sort` VALUES (10013, \'冯九1\', 23, \'2020-01-07 12:23:11\', 47);
INSERT INTO `test_sort` VALUES (10014, \'李四1\', 23, \'2020-01-07 12:23:11\', 48);
INSERT INTO `test_sort` VALUES (10015, \'王五1\', 23, \'2020-01-07 12:23:11\', 21);
INSERT INTO `test_sort` VALUES (10016, \'赵六1\', 23, \'2020-01-07 12:23:11\', 22);
INSERT INTO `test_sort` VALUES (10017, \'钱七1\', 23, \'2020-01-07 12:23:11\', 23);
INSERT INTO `test_sort` VALUES (10018, \'刘八1\', 23, \'2020-01-07 12:23:11\', 24);
INSERT INTO `test_sort` VALUES (10019, \'冯九1\', 23, \'2020-01-07 12:23:11\', 25);
INSERT INTO `test_sort` VALUES (10021, \'测试\', 23, \'2020-01-07 12:23:11\', 28);
INSERT INTO `test_sort` VALUES (10022, \'测试\', 23, \'2020-01-07 12:23:11\', 30);
INSERT INTO `test_sort` VALUES (10023, \'测试\', 23, \'2020-01-07 12:23:11\', 32);
INSERT INTO `test_sort` VALUES (10024, \'测试\', 23, \'2020-01-07 12:23:11\', 33);
INSERT INTO `test_sort` VALUES (10025, \'测试\', 23, \'2020-01-07 12:23:11\', 34);
INSERT INTO `test_sort` VALUES (10026, \'测试\', 23, \'2020-01-07 12:23:11\', 37);

这里在数据插入时，我通过 Navicat 手动修改了表中 sort 字段的值，改成一个比原来最大值。此时再重新添加数据，当自增键的值增长到该值时，就会报该错误。