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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: Number of bytes in binary string

    Return type: int

    For 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 substring.

    Return type: bytea

    For 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: Location of specified substring

    Return type: int

    For 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 substring.

    Return type: bytea

    For 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 substring.

    Return type: bytea

    For example:

    mogdb=# SELECT substr(E'Th\\000omas'::bytea from 2 for 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

    For 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

    For example:

    mogdb=# SELECT btrim(E'\\000trim\\000'::bytea, E'\\000'::bytea) AS RESULT;
       result   
    ------------
     \x7472696d
    (1 row)
  • get_bit(string, offset)

    Description: Extracts bit from string.

    Return type: int

    For example:

    mogdb=# SELECT get_bit(E'Th\\000omas'::bytea, 45) AS RESULT; 
     result
    --------
          1
    (1 row)
  • get_byte(string, offset)

    Description: Extracts byte from string.

    Return type: int

    For example:

    mogdb=# SELECT get_byte(E'Th\\000omas'::bytea, 4) AS RESULT; 
     result
    --------
        109
    (1 row)
  • set_bit(string,offset, newvalue)

    Description: Sets bit in string.

    Return type: bytea

    For example:

    mogdb=# SELECT set_bit(E'Th\\000omas'::bytea, 45, 0) AS RESULT; 
          result      
    ------------------
     \x5468006f6d4173
    (1 row)
  • set_byte(string,offset, newvalue)

    Description: Sets byte in string.

    Return type: bytea

    For example:

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