oracle的substr函数的用法

oracle的substr函数的用法取得字符串中指定起始位置和长度的字符串

substr(string,start_position,[length])
如:
substr('Thisisatest',6,2)wouldreturn'is'
substr('Thisisatest',6)wouldreturn'isatest'
substr('TechOnTheNet',-3,3)wouldreturn'Net'
substr('TechOnTheNet',-6,3)wouldreturn'The'

select substr('Thisisatest', -4, 2) value from dual结果是 te

select substr('emros',-3,1) value from dual 结果是 r

substr('abcde',-6) = null
substr('abcde',-5) = 'abcde'
substr('abcde',-4) = 'bcde'
substr('abcde',-3) = 'cde'
substr('abcde',-2) = 'de'
substr('abcde',-1) = 'e'
substr('abcde',-0) = 'abcde'