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('This is a test', 6, 2)     would return 'is'     substr('This is a test', 6)     would return 'is a test'     substr('TechOnTheNet', -3, 3)     would return 'Net'     substr('TechOnTheNet', -6, 3)     would return 'The'  select substr('Thisisatest', -4, 2) value from dual    结果是   teselect 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'