为什么在MySQL中比较类型不会引发错误？
如果您尝试将字符串与int进行比较，MySQL不会引发错误，因为它将字符串转换为int。让我们首先创建一个表-
mysql> create table DemoTable1852
(
Value1 varchar(20),
Value2 int
);使用插入命令在表中插入一些记录-
mysql> insert into DemoTable1852 values('1John',1);
mysql> insert into DemoTable1852 values('John',1);
mysql> insert into DemoTable1852 values('1',1);
mysql> insert into DemoTable1852 values('John1',1);使用select语句显示表中的所有记录-
mysql> select * from DemoTable1852;
这将产生以下输出-
+--------+--------+ | Value1 | Value2 | +--------+--------+ | 1John | 1 | | John | 1 | | 1 | 1 | | John1 | 1 | +--------+--------+ 4 rows in set (0.00 sec)
这是比较MySQL中类型的查询，它不会引发错误-
mysql> select Value1,Value2, Value1=Value2 as Result from DemoTable1852;
这将产生以下输出-
+--------+--------+--------+ | Value1 | Value2 | Result | +--------+--------+--------+ | 1John | 1 | 1 | | John | 1 | 0 | | 1 | 1 | 1 | | John1 | 1 | 0 | +--------+--------+--------+ 4 rows in set, 3 warnings (0.00 sec)