oracle中substr函数的用法(sqlserver right)

substr('This is a test', 6, 2) would return 'is'
substr('This is a test', 6) would return 'is a test'
substr('TechOnTheNet', 1, 4) would return 'Tech'
substr('TechOnTheNet', -3, 3) would return 'Net'
substr('TechOnTheNet', -6, 3) would return 'The'
substr('TechOnTheNet', -8, 2) would return 'On'

使用RIGHT函数从右边取得指定个数的字符串。
SELECT RIGHT('C:\DATABASE\销售管理系统.MDF',4)
SELECT RIGHT('C:\DATABASE\销售管理系统.LDF',4)
运行结果：
.MDF
.LDF