Binary String Functions and Operators

String Operators

SQL defines some string functions that use keywords, rather than commas, to separate arguments.

• octet_length(string)

  Description: Specifies the number of bytes in a binary string.

  Return type: int

  Example:

  MogDB=# SELECT octet_length(E'jo\\000se'::bytea) AS RESULT;
   result
  --------
        5
  (1 row)

• overlay(string placing string from int [for int])

  Description: Replaces substrings.

  Return type: bytea

  Example:

  MogDB=# SELECT overlay(E'Th\\000omas'::bytea placing E'\\002\\003'::bytea from 2 for 3) AS RESULT;
       result
  ----------------
   \x5402036d6173
  (1 row)

• position(substring in string)

  Description: Specifies the location of a specified substring.

  Return type: int

  Example:

  MogDB=# SELECT position(E'\\000om'::bytea in E'Th\\000omas'::bytea) AS RESULT;
   result
  --------
        3
  (1 row)

• substring(string [from int] [for int])

  Description: Truncates a substring.

  Return type: bytea

  Example:

  MogDB=# SELECT substring(E'Th\\000omas'::bytea from 2 for 3) AS RESULT;
    result
  ----------
   \x68006f
  (1 row)

• substr(string, from int [, for int])

  Description: Truncates a substring.

  Return type: bytea

  Example:

  MogDB=# select substr(E'Th\\000omas'::bytea,2, 3) as result;
    result
  ----------
   \x68006f
  (1 row)

• trim([both] bytes from string)

  Description: Removes the longest string containing only bytes from bytes from the start and end of string.

  Return type: bytea

  Example:

  MogDB=# SELECT trim(E'\\000'::bytea from E'\\000Tom\\000'::bytea) AS RESULT;
    result
  ----------
   \x546f6d
  (1 row)

Other Binary String Functions

MogDB provides common syntax used for calling functions.

• btrim(string bytea,bytes bytea)

  Description: Removes the longest string containing only bytes from bytes from the start and end of string.

  Return type: bytea

  Example:

  MogDB=# SELECT btrim(E'\\000trim\\000'::bytea, E'\\000'::bytea) AS RESULT;
     result
  ------------
   \x7472696d
  (1 row)

• decode(string text, format text)

  Description: Decodes binary data from textual representation. Supported formats are: base64, hex, escape.

  Return type: bytea

  Example:

  MogDB=# SELECT decode('MTIzAAE=', 'base64');
      decode
  --------------
   \x3132330001
  (1 row)

• encode(data bytea, format text)

  Description: Encodes binary data into a textual representation. Supported formats are: base64, hex, escape. escape converts zero bytes and high-bit-set bytes to octal sequences (\nnn) and doubles backslashes.

  Return type: text

  Example:

  MogDB=# SELECT encode(E'123\\000\\001', 'base64');
    encode
  ----------
   MTIzAAE=
  (1 row)

• get_bit(string, offset)

  Description: Extracts bits from a string.

  Return type: int

  Example:

  MogDB=# SELECT get_bit(E'Th\\000omas'::bytea, 45) AS RESULT;
   result
  --------
        1
  (1 row)

• get_byte(string, offset)

  Description: Extracts bytes from a string.

  Return type: int

  Example:

  MogDB=# SELECT get_byte(E'Th\\000omas'::bytea, 4) AS RESULT;
   result
  --------
      109
  (1 row)

• set_bit(string,offset, newvalue)

  Description: Sets bits in a string.

  Return type: bytea

  Example:

  MogDB=# SELECT set_bit(E'Th\\000omas'::bytea, 45, 0) AS RESULT;
        result
  ------------------
   \x5468006f6d4173
  (1 row)

• set_byte(string,offset, newvalue)

  Description: Sets bytes in a string.

  Return type: bytea

  Example:

  MogDB=# SELECT set_byte(E'Th\\000omas'::bytea, 4, 64) AS RESULT;
        result
  ------------------
   \x5468006f406173
  (1 row)