作用: 四舍五入
SELECT CAST('9.0' AS DECIMAL) FROM DUAL; -- 9
SELECT CAST('9.5' AS DECIMAL) FROM DUAL; -- 10
SELECT CAST('9.6' AS DECIMAL) FROM DUAL; -- 10
SELECT CAST('9.3' AS DECIMAL) FROM DUAL; -- 9
SELECT CAST('9.5' AS DECIMAL(10,3)) FROM DUAL; -- 9.500