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The SUBSTRING function, operating like SUBSTR, extracts a character string having the length of substring_length from a position, position, within character string, string, and returns it.

If a negative number is specified to the position value, the SUBSTRING function calculates the position from the beginning of the string. And SUBSTR function calculates the position from the end of the string. If a negative number is specified to the substring_length value, the SUBSTRING function handles the argument is omitted, but the SUBSTR function returns NULL.


SUBSTRING( string, position [, substring_length])

SUBSTRING( string FROM position [FOR substring_length] )


string :

bit string

character string



position :




substring_length :


  • string : Specifies the input character string. If the input value is NULL, NULL is returned.
  • position : Specifies the position from where the string is to be extracted in bytes. Even though the position of the first character is specified as 1 or a negative number, it is considered as 1. If a value greater than the string length is specified, an empty string is returned. If NULL, NULL is returned.
  • substring_length : Specifies the length of the string to be extracted in bytes. If this argument is omitted, character strings between the given position, position, and the end of them are extracted. NULL cannot be specified as an argument value of this function. If 0 is specified, an empty string is returned; if a negative value is specified, NULL is returned.

SELECT SUBSTRING('12345abcdeabcde', -6 ,4), SUBSTR('12345abcdeabcde', -6 ,4);


  '1234'                'eabc'



SELECT SUBSTRING('12345abcdeabcde', 16), SUBSTR('12345abcdeabcde', 16);


  ''                    NULL


SELECT SUBSTRING('12345abcdeabcde', 6, -4), SUBSTR('12345abcdeabcde', 6, -4);


  'abcdeabcde'          NULL