mysql cast与convert 函数的用法

CAST(value as type);
CONVERT(value, type);

mysql> SELECT CONVERT('23',SIGNED);
+----------------------+
| CONVERT('23',SIGNED) |
+----------------------+
|         23 |
+----------------------+
1 row in set

mysql> SELECT CAST('125e342.83' AS signed);
+------------------------------+
| CAST('125e342.83' AS signed) |
+------------------------------+
|             125 |
+------------------------------+
1 row in set

mysql> SELECT CAST('3.35' AS signed);
+------------------------+
| CAST('3.35' AS signed) |
+------------------------+
|           3 |
+------------------------+
1 row in set

DECLARE @dt datetime
  
--单纯的日期
SET @dt='1900-1-2'
SELECT CAST(@dt as binary(8))
--结果: 0x0000000100000000
  
--单纯的时间
SET @dt='00:00:01'
SELECT CAST(@dt as binary(8))
--结果: 0x000000000000012C