substr函数

select substr('Thisisatest', -4, 2) = te

select substr('emros',-3,1)= r

select substr('abcde',-6) = null

select substr('abcde',-5) = 'abcde'

select substr('abcde',-4) = 'bcde'

select substr('abcde',-3) = 'cde'

select substr('abcde',-2) = 'de'

select substr('abcde',-1) = 'e'

select substr('abcde',-0) = 'abcde'