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bit类型在MySQL算作二进制类型，和binary类型类似，只是bit存储的是二进制的数字(0和1).
创建一个表：
create table b(a bit(64));
mysql> insert into b select b'11111111';
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> select repeat(bin(a),8) from b;
+------------------------------------------------------------------+
| repeat(bin(a),8) |
+------------------------------------------------------------------+
| 1111111111111111111111111111111111111111111111111111111111111111 |
+------------------------------------------------------------------+
1 row in set (0.01 sec)
mysql> insert into b select b'1111111111111111111111111111111111111111111111111111111111111111';
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
--查询：
mysql> select bin(a),character_length(a),char_length(a),length(a),a+0 from b;
+------------------------------------------------------------------+---------------------+----------------+-----------+----------------------+
| bin(a) | character_length(a) | char_length(a) | length(a) | a+0 |
+------------------------------------------------------------------+---------------------+----------------+-----------+----------------------+
| 11111111 | 8 | 8 | 8 | 255 |
| 1111111111111111111111111111111111111111111111111111111111111111 | 8 | 8 | 8 | 18446744073709551615 |
+------------------------------------------------------------------+---------------------+----------------+-----------+----------------------+
2 rows in set (0.00 sec)
可以看到bit(64)转为十进制最大为18446744073709551615 ;最值为2的64次方-1.
bit(m)存储的最大值和bigint unsigned 的最值是一样的。
mysql> select bin(a),a+0 from b;
+------------------------------------------------------------------+----------------------+
| bin(a) | a+0 |
+------------------------------------------------------------------+----------------------+
| 11111111 | 255 |
| 1111111111111111111111111111111111111111111111111111111111111111 | 18446744073709551615 |
+------------------------------------------------------------------+----------------------+
2 rows in set (0.02 sec)
mysql> select 18446744073709551615=18446744073709551615;
+-------------------------------------------+
| 18446744073709551615=18446744073709551615 |
+-------------------------------------------+
| 1 |
+-------------------------------------------+
1 row in set (0.00 sec)
mysql> select power(2,8)-1;
+--------------+
| power(2,8)-1 |
+--------------+
| 255 |
+--------------+
1 row in set (0.03 sec)
mysql> select (power(2,64)-1)=18446744073709551615;
+--------------------------------------+
| (power(2,64)-1)=18446744073709551615 |
+--------------------------------------+
| 1 |
+--------------------------------------+
1 row in set (0.01 sec)
可以看到bit(64)存储的最大值和bigint unsigned的最值是一样大的。