How to use SUBSTRING in Oracle database

SUBSTRING, this function is used to find a string of strings, the function of the use of high frequency.
Sample string: "2011-11-17"


The function to ask for a string in Oracle is: SUBSTR
The syntax for the SUBSTR function is:
substr (String, start_position, [length])
String: Source string
Start_position: The starting position of the first character of the substring in the source string
Length: substring lengths
Test results:


1.
substr (' 2011-11-17 ', 0,7)
2011-11
2.
substr (' 2011-11-17 ', 1,7)
2011-11
3.
substr (' 2011-11-17 ', 1,10)
2011-11-17
4.
substr (' 2011-11-17 ', 1,11)
2011-11-17
5.
substr (' 2011-11-17 ', -1,7)
7
6.
substr (' 2011-11-17 ', -8,8)
11-11-17
7.
substr (' 2011-11-17 ', -10,7)
2011-11
8.
substr (' 2011-11-17 ', -11,7)
Null
9.
substr (' 2011-11-17 ',-11)
Null
10.
substr (' 2011-11-17 ',-1)
7
11.
substr (' 2011-11-17 ', 6)
11-17
12.
substr (' 2011-11-17 ', 11)
Null
13.
substr (' 2011-11-17 ', 1,null)
Null
14.
substr (' 2011-11-17 ', null,1)
Null
15.
substr (' 2011-11-17 ', null,null)
Null
16.
substr (' 2011-11-17 ', 1,0)
Null
17.
substr (' 2011-11-17 ', 1,-1)
Null
18.
substr (' 2011-11-17 ', 11,11)
Null



Oracle stipulates:
1) When start_position==0, the starting position of the substring is 1, that is, starting from the first character;
2 when start_position<0, the start position of the string is pushed back from the end of the tail.
3) The length parameter can be default.