SUBSTRING

SUBSTRING(str, start_index, len)

Takes a substring of the specified string, starting at the specified index, of the specified length. start_index = 1 specifies the first character of the string, start_index = -1 specifies the last character of the string. start_index = 0 causes the function to return empty string. If start_index is positive and greater than the length of the string, returns an empty string. If start_index is negative, and has an absolute value greater than the length of the string, the behavior is equivalent to start_index = 1.

For example:

SUBSTRING('hello world', 1, 5) =='hello'
SUBSTRING('hello world', -5, 7) =='world'
SUBSTRING('hello world', -20, 8) =='hello wo'
SUBSTRING('hello world', 0, 10) ==''