SQL常用函数之cast

类型强转：
CAST (<expression> AS <data_ type>[ length ])；cast( 列名/值 as 数据类型 )
e.g. cast(phone as varchar/integer/int)
可以直接执行四舍五入的操作；
--截断小数SELECT CAST('123.447654' AS decimal(5,2)) as result from tab_nm; RESULT
-----------
 123.45
decimal(5,2)表示值总位数为5，精确到小数点后2位。
SELECT CAST('123.4' AS decimal) as result from dual;

结果是一个整数值：123；
还可以用于时间的转换：
2018-3-21 10:40:09
dateselect cast(date as varchar) as date from  table1;结果如下：date2018-3-21 10:40:09
select cast(date as date) as date from  table1;结果如下：date2018-3-21select cast(date as time) as date from  table1;结果如下：date
10:40:09