MySQL中auto_increment（整数）的限制是什么？
auto_increment整数的限制取决于列数据类型。显示如下：
The data type TINYINT range is 127 The data type UNSIGNED TINYINT range is 255 The data type SMALLINT range is 32767 The data type UNSIGNED SMALLINT range is 65535 The data type MEDIUMINT range is 8388607 The data type UNSIGNED MEDIUMINT range is 16777215 The data type INT range is 2147483647 The data type UNSIGNED INT range is 4294967295 The data type BIGINT range is 9223372036854775807 The data type UNSIGNED BIGINT range is 18446744073709551615
让我们以TINYINT为例。如果您给出的值超过127，则MySQL将给出错误。
让我们首先创建一个表。创建表的查询如下。在这里，ID为auto_incerement：
mysql> create table LimitOfAutoIncrement -> ( -> Id TINYINT NOT NULL AUTO_INCREMENT, -> PRIMARY KEY(Id) -> );
仅插入127条记录，这是TINYINT中auto_increment的限制。查询如下：
mysql> insert into LimitOfAutoIncrement values(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(); Records: 127 Duplicates: 0 Warnings: 0
使用select语句显示表中的所有记录。查询如下：
mysql> select *from LimitOfAutoIncrement;
以下是输出：
+-----+ | Id | +-----+ | 1 | | 2 | | 3 | | 4 | | 5 | | 6 | | 7 | | 8 | | 9 | | 10 | | 11 | | 12 | | 13 | | 14 | | 15 | | 16 | | 17 | | 18 | | 19 | | 20 | | 21 | | 22 | | 23 | | 24 | | 25 | | 26 | | 27 | | 28 | | 29 | | 30 | | 31 | | 32 | | 33 | | 34 | | 35 | | 36 | | 37 | | 38 | | 39 | | 40 | | 41 | | 42 | | 43 | | 44 | | 45 | | 46 | | 47 | | 48 | | 49 | | 50 | | 51 | | 52 | | 53 | | 54 | | 55 | | 56 | | 57 | | 58 | | 59 | | 60 | | 61 | | 62 | | 63 | | 64 | | 65 | | 66 | | 67 | | 68 | | 69 | | 70 | | 71 | | 72 | | 73 | | 74 | | 75 | | 76 | | 77 | | 78 | | 79 | | 80 | | 81 | | 82 | | 83 | | 84 | | 85 | | 86 | | 87 | | 88 | | 89 | | 90 | | 91 | | 92 | | 93 | | 94 | | 95 | | 96 | | 97 | | 98 | | 99 | | 100 | | 101 | | 102 | | 103 | | 104 | | 105 | | 106 | | 107 | | 108 | | 109 | | 110 | | 111 | | 112 | | 113 | | 114 | | 115 | | 116 | | 117 | | 118 | | 119 | | 120 | | 121 | | 122 | | 123 | | 124 | | 125 | | 126 | | 127 | +-----+ 127 rows in set (0.00 sec)
现在，您不能插入auto_increment的记录。如果您尝试尝试，则会产生错误：
mysql> insert into LimitOfAutoIncrement values(); ERROR 1062 (23000): Duplicate entry '127' for key 'PRIMARY'