convert string to int return wrong result.

[crazycs520]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.
   In TiDB

mysql root@127.0.0.1:test> SELECT CAST('125e342.83' AS signed);
+------------------------------+
| CAST('125e342.83' AS signed) |
+------------------------------+
| -1                           |
+------------------------------+
1 row in set
Time: 0.006s
mysql root@127.0.0.1:test> SELECT CAST('125e342.83' AS signed);
+------------------------------+
| CAST('125e342.83' AS signed) |
+------------------------------+
| -1                           |
+------------------------------+
1 row in set
Time: 0.006s

In MySQL

mysql root@127.0.0.1:test> SELECT convert('125e342.83' , signed);
+--------------------------------+
| convert('125e342.83' , signed) |
+--------------------------------+
| 125                            |
+--------------------------------+
1 row in set
Time: 0.007s
mysql root@127.0.0.1:test> SELECT CAST('125e342.83' AS signed);
+------------------------------+
| CAST('125e342.83' AS signed) |
+------------------------------+
| 125                          |
+------------------------------+

[zz-jason]

nice catch! how did you find it?

[crazycs520]

when I try to do this issue...#7390

[zz-jason]

👍