substr(aaabbbbvvvcccc,1,4)='2009'

这是Oracle的用法将xc_qj这个字段的数据从第一位开始截取四位

语法

substr( string,start_position,[ length ] )

说明：
string is the source string.
start_position is the position for extraction. The first position in the string is always 1.
length is optional. It is the number of characters to extract. If this parameter is omitted,substr will return the entire string.

start_position用负数则从右边开始数第几个位置

举例: substr('This is a test',6,2)would return 'is' substr('This is a test',6)would return 'is a test' substr('TechOnTheNet',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'