我正在测试插入选择查询并注意到一个奇怪的结果。
CREATE TABLE `test` (
`cnt` int(11) NOT NULL AUTO_INCREMENT,
`a` int(11) DEFAULT NULL,
`b` int(11) DEFAULT NULL,
PRIMARY KEY (`cnt`)
)
CREATE TABLE `test_current` (
`a` int(11) DEFAULT NULL,
`b` int(11) DEFAULT NULL
)
首先我创建了两个表,并将一些值插入到 test_current
mysql> insert into test_current (a,b) values (1,1),(2,2);
Query OK, 2 rows affected (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 0
我做了这个查询
mysql> INSERT INTO test (a,b) SELECT a,b FROM test_current;
Query OK, 2 rows affected, 1 warning (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 1
mysql> select * from test;
+-----+------+------+
| cnt | a | b |
+-----+------+------+
| 1 | 1 | 1 |
| 2 | 2 | 2 |
+-----+------+------+
2 rows in set (0.00 sec)
但是当我再次查询时
mysql> INSERT INTO test (a,b) SELECT a,b FROM test_current;
Query OK, 2 rows affected, 1 warning (0.00 sec)
Records: 2 Duplicates: 0 Warnings: 1
mysql> select * from test;
+-----+------+------+
| cnt | a | b |
+-----+------+------+
| 1 | 1 | 1 |
| 2 | 2 | 2 |
| 4 | 1 | 1 |
| 5 | 2 | 2 |
+-----+------+------+
自动增量只是跳过了 cnt 3。我想知道这是怎么回事。